How to Change Toilet Flush: Full DIY Guide

When your toilet doesn’t flush properly, or you hear water running for no reason, it is more than a small annoyance. A worn flush valve, syphon, or flush button can waste hundreds of litres of water each week and push up your bills. A faulty flush system in your toilet may lead to water wastage and higher bills, but the good news is you can change toilet flush parts yourself with basic tools and a bit of care.

This guide walks you through everything you need: how to spot common problems, how to choose the right toilet flush mechanism, and clear steps to replace a toilet flush valve, syphon, handle, or chain. You will see when a simple toilet chain replacement is enough and when replacing flushing mechanism in toilet is the better choice.

Quick Answer: How to Change Toilet Flush

Changing a toilet flush mechanism is a simple project for many homeowners. If you can use a screwdriver, pliers, and an adjustable wrench, you can likely do it.

10‑Step Summary to Replace a Toilet Flush Valve or Syphon

Here is a short guide before we break each stage down in detail. This applies to most close‑coupled toilets where the cistern (tank) sits directly on the toilet bowl.

Before starting any repair work, make sure to turn off the water supply by using the toilet shut-off valve located beside or behind the toilet.
After flushing the toilet to empty the cistern, you may need to remove the float valve to prevent any remaining water from spilling.
Remove the cistern lid and set it somewhere safe where it cannot fall or crack.
To remove the fill valve, start by disconnecting the water supply line, then remove the float valve by unscrewing the fixing nut beneath the tank.
Loosen and remove the nuts that hold the tank to the bowl, then lift the tank off the toilet and place it on a flat surface.
To remove the flush valve, use a wrench to unscrew the fixing that secures the valve from underneath the tank.
Remove the old flush valve (or syphon) and the old doughnut seal found between the toilet bowl and the cistern. Clean the area.
Install the new flush valve or syphon through the hole at the bottom of the cistern, fit the new doughnut gasket, and tighten the mounting nut by hand and then gently with a wrench.
Re‑fit the tank onto the bowl, refit the bolts, and reconnect the water supply line.
Turn the water back on, let the toilet tank fill with water, then test the flush and check all joints for any leak.

That is the core process to replace a toilet flush valve or syphon.

How Long Does It Take to Change a Toilet Flush?

Most people with basic DIY skills can replace a toilet flusher in about:

30–60 minutes for a normal close‑coupled toilet
60–90 minutes if the bolts are rusty or access is tight
Longer for wall‑hung or concealed cisterns, which are more complex

Often, the slowest part is dealing with old, corroded nuts and bolts.

Tools, Skill Level, and Safety at a Glance

To change toilet flush parts you usually need:

An adjustable wrench or small spanner set
A flathead and Phillips screwdriver
Pliers (helpful for stubborn nuts)
A sponge, bucket, and old towels
Plumber’s tape (PTFE tape) for threaded joints
A new flush valve, syphon, or flush unit, plus a new doughnut seal and tank bolts

The job is beginner to intermediate. You do not need formal plumbing training, but you should be comfortable working carefully around porcelain, which can crack if over‑tightened or knocked. Before proceeding, check to make sure you have all necessary tools, and ensure the workspace is clear to avoid accidents.

Work slowly, support the tank with your hands when lifting or tilting, and never force porcelain parts.

When a Quick Flush Repair Isn’t Enough (Replace vs Repair)

Sometimes you can fix a running toilet or weak flush by adjusting the chain, changing the flapper, or tweaking the water level inside the cistern. At other times, you need to replace a toilet flush valve or the entire flush mechanism.

Here is a simple way to think about it:

Situation	Likely Fix
Chain snapped or slipped off, handle loose	Toilet chain replacement or toilet flush handle replacement
Flapper warped or not sealing, but valve body looks fine	Replace flapper only
Toilet constantly runs even with new flapper, valve body cracked, or overflow height is wrong	Replace a toilet flush valve / syphon
Water leaking between tank and bowl	New doughnut seal and often new flush unit

If you have tried a basic toilet chain replacement or a simple flapper swap and the toilet still doesn’t flush well or keeps running, it is time to change the full mechanism.

Before You Start: Tools, Parts, and Compatibility Checks

Before you grab a wrench, it helps to know what type of toilet flush you have and what kind of new toilet flush valve or syphon will fit.

Essential Tools and Materials for Toilet Cistern Repair

For most toilets you will need:

An adjustable wrench or spanner set for the nuts on the bottom of the tank and water supply line
A flathead screwdriver for older flush handles or clips, and a Phillips screwdriver for tank bolts
Plumber’s tape to help form a watertight seal on metal threads
A sponge, bucket, and a few towels to catch water when you turn off the water supply and disconnect hoses
A replacement flush valve or syphon, a new doughnut gasket (seal) found between the toilet tank and bowl, and new tank bolts with rubber washers
Optional: penetrating oil for rusty bolts, and thin work gloves for grip

Setting these out beside the toilet before you start makes the job much smoother.

Choosing the Right Flush Valve or Syphon for Your Toilet

Not all toilet flush valves are the same. To avoid surprise problems, check:

How the water enters the cistern: side‑entry or bottom‑entry fill valve
Whether you have a lever handle on the side or a flush button on the top
Whether the toilet is single flush (one volume) or dual flush (a half flush and full flush)

The new part must match both the type of flush and the height inside the cistern. The overflow tube on the new unit must sit above the normal water line but below any holes in the cistern wall. Many modern toilets use “universal” flush valves that can be adjusted up and down, but you still need to match the connection style and diameter at the bottom of the cistern.

In short, when you plan to replace a toilet flush valve, check:

Cistern depth from bottom to top
Size of the hole where the valve from the toilet passes through
Whether you have a button flush or lever so the actuator matches

Lifting the Lid: Identifying Your Existing Flush Mechanism

Take off the cistern lid and look inside the cistern. You will see:

A fill valve (or float valve) on one side. This valve controls the water level inside the cistern.
A central flush valve or syphon that lets water drop into the toilet bowl when you flush.
Some kind of link between the flush handle or flush button and the valve, such as a chain, plastic arm, or cable.

Common setups include:

Flapper-style flush valve: A rubber flapper lifts off a circular flush valve opening when the handle pulls a chain.
Canister or tower valve: A tall cylinder rises to allow water through.
Traditional syphon: Often found in older toilets, especially with a lever. A full syphon unit lifts water over a bend.

If the top of the cistern has two buttons (small and large), you have a dual‑flush system. If there is just one button or one side lever, it is a single‑flush toilet.

Safety and Shut‑Off: Preparing the Work Area

Before you touch any nuts or bolts, find and test the shut‑off valve:

Look at the side of the toilet near the floor for a small valve on the water supply line.
Turn it clockwise to turn off the water. If it is stiff, move it gently back and forth once or twice.
Flush the toilet and check that the tank does not refill. If it still does, the isolation valve may be faulty and you may need to turn off the water to the whole house at the main stop tap.

Lay a towel around the base of the toilet to catch drips, open a window for fresh air, and clear any items from around the toilet so you can move freely. A calm, tidy space helps you avoid dropping parts or bumping the tank.

Understanding Toilet Flush Mechanisms and Common Problems

Knowing how the parts work makes it much easier to see how to replace toilet flusher parts and decide what to change.

Gravity Flush, Pressure‑Assisted, and Dual‑Flush Explained

Most homes use one of these types of toilet flush:

Gravity flush: The most common. Water stored in the cistern flows down by gravity when the valve opens. The height of the cistern and size of the flush valve opening control power.
Pressure‑assisted: Uses air pressure in a sealed tank inside the cistern. These are noisier but give a strong flush. They are less common in homes and often better left to professionals if they fail.
Dual‑flush: Uses two different water volumes. The small button gives a half flush (often around 3 litres) and the large button gives a full flush (often around 6 litres). This helps save water.

For most of this guide we focus on gravity and dual‑flush toilets, since these are the ones most people will repair at home.

Inside the Cistern: Flush Valve, Syphon, Flapper, and Fill Valve

Inside your tank, each part has a job:

The fill valve (or float valve) lets water in and shuts it off when the right level is reached.
The flush valve or syphon holds water in the tank until you flush, then opens to release it.
A flapper or seal at the bottom of the valve stops leaks between flushes.
The flush handle or button moves a lever arm, rod, cable, or chain to lift the valve or flapper.

When you press the flusher or push the toilet flush button, water drops rapidly through the central hole into the toilet bowl, carrying waste away. Then the fill valve refills the cistern for the next flush.

Typical Symptoms of a Failing Flush System

If you are thinking about replacing your toilet flush, you likely see at least one of these:

Weak flush that needs two or three attempts
Frequent clogs, even with normal use
A running toilet sound long after you flush
Occasional “ghost flushes” where the toilet refills by itself
Water pooling around the seal found between the toilet bowl and the cistern
A handle that feels loose or a button that sticks down

These problems can come from a worn flapper, cracked valve body, bad doughnut seal, faulty fill valve, or a simple chain issue.

How to Diagnose Whether the Flush Valve, Syphon, or Fill Valve Is to Blame

To narrow it down, you can use a few simple tests:

Food dye test: Add a few drops of food colouring into the cistern and wait 10–15 minutes without flushing. If coloured water appears in the bowl, the flush valve may be leaking around the flapper or seal.
Handle resistance test: If the handle moves but feels very loose and the toilet doesn’t flush, the chain may have come off or snapped. If the handle is very stiff, parts of the flush mechanism may be stuck or broken.
Tank level check: After refilling, watch the water level inside the cistern. If it rises above the overflow pipe and then drains away, the fill valve is not shutting off. If the water never reaches the marked level, you may have a fill valve problem or an incorrectly set float.

People often ask, How do I know if my toilet flush valve is bad? In simple terms, if the flapper is new, the chain is set correctly, and you still get constant leaks into the bowl, or the valve body looks cracked or warped, then it is time to remove the flush unit and fit a new one.

Detailed DIY: Removing the Old Flush Valve or Syphon

Once you know you need a new toilet flush valve or syphon, it is time to remove the old system. Take your time and protect the porcelain.

Shut Off Water, Drain Cistern, and Access Components

Turn the toilet shut‑off valve clockwise to turn off the water supply. Flush the toilet to drain the toilet tank. Hold the handle down for a moment to let as much water out as possible.

There will still be remaining water in the tank, sitting at the very bottom around the valve. Use a sponge and small container to remove this so you are not working in a puddle. A dry tank makes it easier to see parts and keep your hands safe.

Carefully lift off the cistern lid. Some lids on press button flush toilets are held by the button assembly. In that case, you may need to unscrew the fixing screw at the top of the cistern inside the button, or unscrew the button collar by hand before lifting the lid. Take your time; do not pry hard with tools on porcelain.

Set the lid somewhere stable where it cannot be knocked.

Disconnecting the Water Supply and Tank Fixings

Now look under the tank. You will see:

The water supply line connected to the fill valve thread
One or two tank‑to‑bowl bolts with nuts and washers

Place a towel or small bucket under these points. Use an adjustable wrench or pliers to loosen the coupling nut on the water supply line and disconnect the water supply from the fill valve. When loosening the coupling nut on the water supply line, remember that the material could be metal or plastic, and this may affect the type of tool and the amount of pressure needed.

Next, hold the tank bolts inside the cistern with a screwdriver, and from below, loosen and remove the nuts. Old bolts can be very rusty. A little penetrating oil, left for 10–15 minutes, often helps. If the nuts will not move at all, you may need to carefully cut them with a hacksaw or a small rotary tool, but do this slowly to avoid touching the porcelain.

Once the nuts and washers are off, gently rock the tank to break the seal, then lift the tank straight up off the bowl. This is easier with two people, especially if the tank is heavy. Place the tank on a towel or cardboard on the floor or a sturdy work surface.

Removing the Existing Flush Valve or Syphon Unit

Now, turn the tank so you can see the bottom of the tank. In the centre you will see the large plastic nut that holds the flush valve from the toilet in place. Use a large adjustable wrench, spanner, or your hand to unscrew this nut anticlockwise. It may be tight, but avoid using so much force that you crack the tank.

Once the nut is off, push the valve up slightly from below and then lift it out from the top of the cistern. This removes the old system: the valve body, overflow pipe, and any seals.

Pull off the thick rubber doughnut seal that sits on the base where the tank meets the bowl. This is the seal found between the toilet bowl and the cistern. It may be stuck, so peel it away and clean the porcelain around it. Wipe both the underside of the tank and the top of the bowl so the new gasket can sit flat and form a watertight seal.

Common Removal Challenges and How to Solve Them

Many people get stuck because of:

Rusted tank bolts: If penetrating oil does not help, careful cutting is often the only option. Work slowly, and stop if the blade touches porcelain.
Stuck mounting nuts: A longer wrench or a pair of pliers to grip the nut can help. Sometimes gently tapping the wrench with your hand will start it moving.
Hairline cracks: If you notice cracks in the tank once it is off, do not over‑tighten new parts. In some cases, a cracked tank is a sign it is time for full toilet replacement rather than more repairs.

If the tank is badly damaged or you feel unsure, this is a sensible point to consider calling a plumber.

Installing the New Flush Mechanism for a Strong, Efficient Flush

With the old unit out, you can install the new flush valve or syphon and bring your toilet back to full strength.

Fitting the New Flush Valve or Syphon and Gasket

Start by checking the new flush unit for any adjustable height settings. If it is adjustable, set it so the top of the overflow tube is about one inch (2–3 cm) below the top of the tank and above the expected water line. This helps stop accidental spills while still giving a strong flush.

Place any rubber gasket or flat washer that came with the valve onto the valve’s base from inside the tank, as the instructions state. Then insert the valve through the hole at the bottom of the cistern, making sure it sits straight.

From underneath the tank, fit the large mounting nut on the threaded part of the valve and turn it clockwise. Tighten by hand first, then snug it up with a wrench. The key point is tight but not extreme; over‑tightening can crack the porcelain or deform the gasket.

Push the new doughnut seal onto the valve base so it sits between the tank and bowl area. This thick ring creates the main water seal between tank and toilet bowl. Make sure it is even all the way around.

If the new valve has any metal threads that will connect to a metal coupling, you can wrap two to three turns of plumber’s tape on those threads to help create a watertight seal.

Reassembling the Tank and Reconnecting the Water Line

Carefully lift the toilet tank back onto the bowl, ensuring the flush valve tailpiece lines up correctly and guide the bolts into their holes for a secure fit. The doughnut gasket should sit gently on the raised ring on the bowl.

From below, add the rubber washers, then metal washers, then nuts to the tank bolts in the order the instructions suggest. Tighten each nut a few turns at a time, alternating from one side to the other. This pulls the tank down evenly so it does not rock.

Stop tightening as soon as the tank feels stable and does not move when you press on it. If you notice the porcelain starting to strain or hear any creaks, you are too tight.

Next, reconnect the water supply line to the fill valve. Use your fingers to start the connection so you do not cross‑thread the nut, then finish with a wrench. Again, snug is enough.

Adjusting the Chain, Handle, and Dual‑Flush Buttons

Now reconnect the chain or rods between the flush handle or flush button and the new valve:

For a toilet flush handle replacement with a flapper valve, hook one end of the chain to the lever arm inside the tank and the other end to the flapper. You want a little slack so the flapper can close, but not so much that pressing the handle barely lifts it. Usually 6–12 mm (about a quarter inch) of slack is right. This is how you reattach toilet chain to flapper.
For button flush systems with a tower valve, adjust the plastic rods or cables so that pressing the button fully lifts the valve, but the valve can still drop freely and seal.

If your press button flush toilet has separate buttons for half flush and full flush, test both. A new toilet flush might need a few adjustments before the buttons line up just right.

Many people ask, Is it easy to change a toilet flush button? If the cistern is already open, swapping a top‑mounted button unit is usually simple: you unscrew the fixing collar, lift the old button, reconnect the new cable or rod to the valve, and screw in the new trim. The hardest part is often adjusting the rods so they are not too long or too short.

Testing, Fine‑Tuning, and Fixing Post‑Installation Issues

Your new flush is in, but you are not finished until you confirm there are no leaks and the flush power feels right.

First Fill and Leak Check: What to Look For

Turn the shut‑off valve counter‑clockwise to turn the water back on. Watch the toilet tank with water as it fills:

Check under the tank around the flush valve nut and tank bolts.
Check the join between the tank and bowl, where the doughnut seal sits.
Look at the fill valve joint and the supply hose connection.

If you see drips, lightly tighten the nearest nut a small amount and watch again. Often a quarter turn is enough.

A normal fill should take under a minute for most toilets, maybe a bit more if water pressure is low. If water never stops, lift the float by hand. If that stops the flow, you need to adjust or repair the fill valve. If water flows into the bowl constantly even when the fill valve stops, recheck the flush valve seal.

People often ask, Why is my toilet still running after changing the flush? The usual reasons are:

Chain too tight, holding the flapper or seal open
New valve not seated flat on the tank bottom
Debris caught under the new seal
Fill valve set too high, so water runs into the overflow

All of these are easy to adjust.

Adjusting Water Level, Flush Strength, and Refill Speed

Most fill valves have a small screw or clip you can move up or down to change the water level. Set the water line to match the mark inside the cistern if there is one. If not, aim for about 2–3 cm below the top of the overflow tube.

For a water‑saving toilet flush, you can often lower the level a bit compared with the old setting. Just be sure that the flush still clears the bowl in one go. If you have to flush twice often, you are not really saving water.

Some modern valves let you change how quickly the tank refills. This is less important in most homes, but can help reduce noise.

Troubleshooting Common New‑Install Problems

If your new toilet flush valve still feels wrong, here are common issues and simple fixes:

Weak flush after replacement: Check that the valve is fully opening. The lever or button may not be lifting it enough. Adjust the chain, rods, or cables. Also check for partial blockages in the rim holes of the bowl or in the waste line.
Intermittent leaks: If you spot small drips only sometimes, the gasket might not be seated evenly. You may need to drain the tank, unscrew the nuts slightly, adjust the seal positions, and re‑tighten evenly.
Handle sticking or not returning: Make sure the handle nut inside the tank is not too tight and that the lever arm is not rubbing against the tank wall. Lubricate any metal‑on‑metal contact lightly if allowed by the manufacturer.
Buttons not returning on a button flush: Check that the rods or cables are straight and not bent or twisted. They should move freely when you press and release the buttons.

If you have gone through these checks and still have trouble, you can take a quick video and show it to a plumber for advice, or decide to book a visit.

When to Call a Professional Plumber After DIY Attempts

There is no shame in calling for help. You should consider a professional if:

You see new cracks in the tank or bowl
The toilet rocks or feels unstable at the floor
You have a pressure‑assisted or concealed flush system
You cannot stop a leak even after reseating seals and re‑tightening

For many people, the cost of one call‑out is less painful than living with a small but steady leak or repeated stress.

Costs, Time, and Water‑Saving Benefits of a New Toilet Flush

Changing your flush mechanism is not just about comfort. It can save real money and help reduce water use.

Parts and Labor: How Much Does It Cost to Change a Toilet Flush?

Typical costs for parts and labor are:

Flush valves or syphon kits: about £20–£50 for standard units with seals and bolts
Plumber labor: around £50–£150 depending on where you live and how complex the job is

So, if you do your own valve replacement, you often only pay for the part. If you hire a plumber, you pay for both parts and labor, but you get speed and experience.

Time Investment: Realistic DIY Timeframes

Most people should plan:

30–60 minutes for a standard close‑coupled toilet with normal bolts
Up to 90 minutes for older toilets with seized bolts or awkward access
More time for wall‑hung toilets or hidden cisterns, which are usually not first‑time DIY jobs

Allow yourself a calm afternoon the first time you replace a toilet flush, so you do not feel rushed.

Water Efficiency: How a New Flush Mechanism Saves Money

An old, leaking valve can waste huge amounts of water. Even a small trickle can add up to thousands of litres a year. Newer flush systems often use less water per flush while still clearing the bowl well.

Many modern dual‑flush setups use about 3 litres for a half flush and around 6 litres for a full flush, which is much less than older high‑volume toilets. Reducing water consumption not only lowers bills but also contributes to water conservation. According to the EPA’s WaterSense Program, water-efficient toilets can help save thousands of gallons per year, promoting environmental sustainability and cost reduction. If you fix a leak and reduce each flush by even 1–2 litres, the annual savings in water and cost can be significant, especially for larger households.

Environmental Impact and Official Guidelines

Saving water does more than trim your bill. Water treatment and pumping use energy, so cutting waste can lower your indirect carbon footprint. In many regions, water agencies encourage efficient toilet flush settings and support water‑saving toilet flush upgrades.

If you want to check local advice or rules on plumbing work, it is worth looking at guidance from your national or regional environmental or building bodies (examples are linked at the end of this guide).

Final Checks, Maintenance Tips, and Key Takeaways

Take a moment to ensure everything is in top shape with your toilet flush system. A quick round of checks can confirm that everything is functioning smoothly and efficiently. This section covers the final inspection steps, essential maintenance tips, and key takeaways that will help you extend the life of your flush system and avoid unnecessary repairs down the road.

Final Inspection Checklist Before You Put the Lid Back On

Before you walk away, stand back and check:

The tank and bowl connection is dry and stable
No drips from the bottom of the cistern, bolts, or water supply joints
The water level stops at the right height
The handle or button works smoothly and returns by itself
One press gives a clean, complete flush without splashing

Once you are satisfied, replace the cistern lid and clean up tools and towels.

Simple Maintenance to Extend the Life of Your New Flush Mechanism

To keep your new toilet flush working well:

Avoid drop‑in bleach tablets or very harsh chemicals inside the cistern, because they can damage rubber seals and plastic parts
Every few months, open the lid and check the chain, seals, and water level
If you notice early signs of a leak or weak flush, deal with them sooner rather than later

A few minutes of simple checks can add years to the life of your flush system.

Core Lessons: Safe, Efficient, and Cost‑Effective Flush Upgrades

To change toilet flush parts safely, remember this simple path:

Shutoff – Turn off water and empty the tank.
Remove – Take off the lid, disconnect the supply, and remove the tank if needed.
Replace – Swap the valve, syphon, gasket, or chain with a compatible part.
Reseal – Set gaskets carefully and tighten nuts evenly.
Test – Refill, check for leaks, and test the flush.
Fine‑tune – Adjust chains, buttons, and water level.

Once you have done this once, you may be surprised how easy future toilet repairs feel.

Next Steps: When to Consider a Full Toilet Replacement

Sometimes, replacing the flush parts is not enough. You might think about a full toilet replacement when:

The bowl design clogs often, even with a strong flush
The porcelain is cracked, stained, or badly damaged
The toilet is very old and uses far more water than modern models

If that is your situation, your next step is to learn how to choose a high‑efficiency toilet with a strong, reliable flush that suits your home. Until then, a well‑fitted new flush valve and good seals can give your current toilet many more useful years.

FAQs

1. Can You Change the Flush on a Toilet?

Yes. In many homes, you can change toilet flush parts yourself. Simple jobs like toilet flush handle replacement, toilet chain replacement, changing a flapper, and even a full flush valve swap are within reach of a careful DIYer. You just need to follow the steps to turn off the water supply, remove the tank (when required), and work gently with the porcelain.

2. How to Change a Toilet Bowl Flush?

To change a toilet bowl flush, you replace the parts that control water flow from the tank to the bowl. This usually means:

Turning off water and draining the toilet tank
Removing the tank from the bowl
Swapping out the flush valve or syphon and doughnut seal
Re‑installing the tank and adjusting the handle or button

Once the new flush mechanism is in place, your toilet should clear the bowl more strongly and use the right amount of water.

3. Is It Easy to Change a Toilet Flush Button?

In many press button flush toilets, changing the button is one of the easier tasks. With the cistern lid off, you normally:

Unscrew the ring that holds the old button
Lift the old button and disconnect any rod or cable
Fit the new flush button, reconnect its rod or cable to the valve, and screw the ring back on

The tricky part is making sure the rods are the right length so the system allows full lift without pressing constantly on the valve. A few test flushes will show whether it is set correctly.

4. Can You Replace a Toilet Flush Valve Without Removing the Tank?

People often hope they can replace a toilet flush valve without removing the tank. In most two‑piece toilets, the answer is no. The valve is held in place by a large nut under the tank and a seal that sits between tank and bowl, so you must remove the toilet tank to reach it safely.

The only time you skip tank removal is when you are changing just the flapper or doing a toilet chain replacement, since these parts are accessible from inside the cistern.

5. Can I Replace a Flush Valve Myself?

Yes, many homeowners replace a toilet flush valve themselves. As long as you:

Can identify the right replacement part
Are able to turn off the water and safely lift the tank
Are patient with tight nuts and rusty bolts

then you can do this without special tools beyond a wrench, screwdriver, pliers, and some towels.

6. Can You Replace a Toilet Chain? How to Fix a Toilet with a Broken Chain?

A broken chain is one of the simplest fixes. To fix a toilet with a broken chain:

Turn off the water if you like, or just close the lid so nothing falls in.
Lift the cistern lid.
Clip one end of the new chain to the flush handle arm or button lever.
Clip the other end to the flapper or valve lift point.
Adjust the length so the flapper can close fully but still lifts when you press the handle.

This is all there is to toilet chain replacement in most common toilets.

References

https://www.epa.gov/watersense