What you are replacing and why it matters

The inside of your toilet tank holds three main parts: the fill valve (which refills the tank after you flush), the flush valve (which releases water into the bowl), and the flapper (a rubber seal that sits on top of the flush valve). When any of these wears out, your toilet will run constantly, leak, or fail to flush properly. Replacing them costs between $15 and $50 in parts and takes 30 to 45 minutes with basic tools.

You do not need a plumber for this job. The parts are standardized, widely available at hardware stores and online, and the work involves no soldering, cutting, or permanent installation. If you can turn a wrench and follow a sequence, you can do this yourself.

Key Takeaways

  • Turn off the water supply at the shutoff valve under the tank, then flush to empty it completely before you start.
  • The flapper is the easiest part to replace first — it sits on top of the flush valve and costs $5 to $10.
  • The fill valve screws in from underneath the tank and requires a large wrench, but removal and installation take less than 10 minutes once you drain the tank.
  • The flush valve sits at the bottom center of the tank and is the hardest to access, but you can replace it without removing the tank if you work from inside.
  • Test the refill and flush cycle before you call the job done — water should stop running after 30 seconds and the bowl should empty completely.

Shutting off water and draining the tank

Locate the shutoff valve on the water line that runs to the toilet. It is usually a small knob or lever on the pipe under the tank, close to the wall. Turn it clockwise (or flip the lever perpendicular to the pipe) until it stops. Do not force it — it should turn smoothly.

Flush the toilet once. The tank will empty and the fill valve will not refill it because the water is now shut off. If water continues to trickle in, the shutoff valve is not fully closed; turn it a bit more. Leave the toilet lid off for the rest of the work so you can see inside the tank clearly.

Replacing the flapper

The flapper is a rubber or plastic disc attached to a chain that hangs from the overflow tube (the hollow pipe in the center of the tank). Look at the bottom of the tank — you will see the flapper sitting on top of a larger piece called the flush valve. The chain connects the flapper to a handle arm that runs to the flush lever on the outside of the tank.

Unhook the chain from the handle arm by squeezing the clip or untwisting the wire that holds it. Lift the flapper off the flush valve — it usually slides up and off two small ears or pegs on the valve. Take the old flapper to the hardware store or note its model number so you buy the exact replacement. Most flappers are universal, but some older tanks use specific sizes.

Slide the new flapper onto the pegs, then reattach the chain to the handle arm. The chain should have a tiny bit of slack — about one-quarter inch — when the handle is at rest. If it is too tight, the flapper will not seal; if it is too loose, the handle will not open it fully. Adjust the clip or wire to get the slack right, then turn the water back on and test the flush.

Replacing the fill valve

The fill valve is the assembly on the left side of the tank (when facing it) that refills the tank after you flush. It screws into the bottom of the tank from underneath. You will need an adjustable wrench or a fill valve wrench (a specialized tool that costs $8 to $12 and makes the job easier).

Reach under the tank and locate the large nut that holds the fill valve in place. Use the wrench to turn it counterclockwise. You may need to hold the valve body steady with your other hand so it does not spin. Once the nut is loose enough, unscrew it by hand. Water may drip — have a towel ready. Lift the old valve out of the tank.

Insert the new fill valve through the hole from inside the tank, then thread the nut onto it from underneath. Tighten it by hand first, then use the wrench to snug it down — firm, but not so hard that you crack the plastic. Reconnect the water supply line by turning the compression nut clockwise. Turn the water back on slowly and watch for leaks around the base of the valve. If water drips from the nut, tighten it another quarter turn.

Replacing the flush valve

The flush valve is the largest component inside the tank — a hollow cylinder that sits at the bottom center. Water drains through it into the bowl when you flush. It is held in place by a large nut underneath the tank, similar to the fill valve. This job is harder because the valve is in the middle of the tank and harder to reach, but it is still doable without removing the tank.

Drain the tank completely (you should have already done this). Reach under the tank and locate the nut holding the flush valve. Use an adjustable wrench to turn it counterclockwise. This nut is often tighter than the fill valve nut because it bears more pressure. You may need to brace the valve from inside the tank with your other hand. Once the nut is loose, unscrew it by hand.

From inside the tank, lift the old flush valve straight up and out. It may be stuck — rock it gently side to side to break the seal. Take note of the rubber gasket (a flat ring) that sits between the valve and the tank bottom. If it is cracked or hardened, replace it with the gasket that comes with the new valve.

Insert the new flush valve through the hole, making sure the gasket sits flat on the tank bottom. Thread the nut onto the valve from underneath and tighten it by hand first. Use the wrench to snug it down firmly. Do not over-tighten — you can crack the plastic. Reconnect the flapper chain if you removed it, then turn the water back on and test.

Testing the refill and flush cycle

Turn the water back on at the shutoff valve. The tank should fill within 30 to 60 seconds and then stop. Listen for the fill valve to shut off — you should hear a click or feel the water pressure drop. If water continues to run, the flapper is not sealing; check that it is sitting flat on the flush valve and that the chain has the right amount of slack.

Flush the toilet. The bowl should empty completely and the tank should refill. If the bowl drains slowly or incompletely, the flush valve may not be opening fully — check that the chain is not too tight and that the flapper is lifting all the way. If water leaks from under the tank, tighten the nut on whichever valve is leaking. Let the tank sit for five minutes and watch for drips — a small amount of condensation on the outside is normal, but a steady drip means a seal is not tight.

Common problems and how to fix them

If the tank fills but does not stop, the flapper is not sealing. The most common cause is a chain that is too tight, pulling the flapper up slightly even at rest. Loosen the chain by one-quarter inch and test again. If the flapper still leaks, the rubber may be hardened or warped — replace it with a new one. Mineral buildup on the flush valve seat (the rim the flapper sits on) can also prevent a seal; clean it with white vinegar and a soft brush before installing a new flapper.

If the bowl does not empty fully, the flush valve is not opening enough. Check that the chain has slack and is not binding. If the chain is fine, the flush valve seat may be clogged with mineral deposits or debris. Turn off the water, remove the flapper, and look inside the flush valve opening. Use a flashlight to see if anything is blocking it. A small piece of debris or mineral crust can prevent the valve from opening fully. Clean it out with a brush or cloth, then reinstall the flapper and test.

If water leaks from under the tank, one of the nuts is not tight enough. Turn off the water, dry the area completely, and identify which valve is leaking by watching where the water comes from. Tighten the nut another quarter turn, turn the water back on, and watch for 10 minutes. If it still leaks, turn off the water again and tighten it another quarter turn. Do not over-tighten in one go — gradual tightening is safer and less likely to crack the plastic.

Tools and parts you will need

You will need an adjustable wrench (or a fill valve wrench, which is optional but helpful), a flathead screwdriver, a towel, and a bucket or cup to catch drips. Parts vary by toilet model, but universal kits that include a flapper, fill valve, and flush valve cost $25 to $50 and are available at any hardware store. If you want to replace only one part, flappers cost $5 to $10, fill valves cost $15 to $25, and flush valves cost $20 to $40. Bring the old part with you to the store or note the toilet brand and model so you get the right fit.

Some older toilets use different valve designs that require specialized tools or parts. If your toilet is more than 20 years old and the parts do not match the descriptions here, take a photo of the inside of the tank and show it to the hardware store staff — they can tell you whether a standard replacement will work or whether you need a specialty part.

Frequently Asked Questions

Do I have to turn off the water to replace the flapper?

No. The flapper is inside the tank, and turning off the water just makes the job cleaner and safer. You can replace the flapper with the water on, but you will have to work quickly and may get wet. Turning off the water and flushing first takes 30 seconds and is worth it.

What if the nut under the tank is stuck and will not turn?

explore penetrating oil (like WD-40) around the nut and let it sit for 15 minutes. Try turning it again with the wrench. If it still will not budge, wrap a cloth around the nut to give the wrench better grip and try once more. Do not force it hard enough to strip the plastic — if it will not move, you may need a plumber to remove it without breaking the tank.

Can I replace all three parts at once?

Yes. If your toilet is old or has had multiple problems, replacing the flapper, fill valve, and flush valve together takes about an hour and costs $40 to $60 in parts. It is often cheaper and faster than replacing them one at a time over several months. Universal kits that include all three are available at hardware stores.

How do I know which part is broken if the toilet is running constantly?

A running toilet is almost always the flapper. Listen to where the water sound is coming from — if it is a hissing or trickling sound inside the tank, the flapper is leaking. If it is a refill sound (like the tank is filling), the fill valve may not be shutting off. The easiest test is to replace the flapper first; if that does not stop the running, move on to the fill valve.

Will I damage the tank if I over-tighten the nuts?

Yes. Plastic tanks can crack if you tighten the nuts too hard. Tighten them firmly by hand first, then use the wrench to snug them down — you should feel resistance, but you should not need to strain. If a nut leaks slightly after tightening, tighten it a quarter turn more rather than a full turn. Gradual tightening is safer than one hard pull.