Leaking Toilet Flapper? How To STOP The Leak!

Last Updated on October 5, 2023 by toilethaven

A leaking toilet flapper is a sign that the flapper is dirty, worn out, or even warped, which prevents it from making a good seal around the flush valve. A worn flush valve or a tight or entangled flapper chain could also cause the problem.

To stop a toilet flapper from leaking, remove and clean it or replace it if worn out, cracked, or warped. If the flush valve is damaged, replace it as well. Also, ensure the flapper chain is not too tight or entangled on anything.


If your toilet still leaks even after replacing the flapper, the flush valve is the culprit. Lift off the toilet flapper and run your finger around the edge of the flush valve opening. If there are nooks or irregularities, the flapper will not seal properly, so replace the flush valve.

To know if your toilet flapper leaks, add some food color or dye inside the toilet tank and wait about 30 minutes without flushing the toilet. If the color appears inside the bowl, you have a leaking flapper.

The most obvious sign that a toilet flapper needs to be replaced is when you have a constantly running toilet. Normally, the toilet flapper is worn out or warped, which is, in most cases, caused by hard water.

Vaseline can be applied on a toilet flapper to soften it when it is hard and no longer sealing correctly. Drain the toilet tank and dry the flapper before applying the Vaseline. This is, however, a temporary solution as you wait to replace it.

If your toilet uses a flush valve seal, it could be warped, cracked, or worn out. Replacing the seal is enough to stop the toilet from leaking.

Before concluding that you have a leaking toilet flapper, remove the toilet tank lid and first check if the flapper chain is too tight or entangled on another part. Ideally, the chain should have a 1/4-1/2 inch slack.

How Do You Stop a Toilet Flapper from Leaking?

The best and long-term way to stop a toilet flapper from leaking is by replacing it with a new one. Removing the debris will stop the leak if the flapper is neither worn out nor warped but just dirty. Replace the flush valve if its rim is irregular, preventing the flapper from sealing.

Here are the steps to follow when fixing a leaking toilet flapper:

  • Turn off the water supply to the toilet. The shut-off valve is on the wall behind the toilet.
  • Flush the toilet.
  • Remove the toilet tank lid and place it away in a safe place where it cannot fall off and crack.
  • Disconnect the flapper chain from the flush handle arm and drop it inside the tank.
  • Unhook the flapper ears from the flush valve pegs and lift it out of the tank.
  • Carefully inspect the flapper.
  • If the flapper is clearly warped and/or cracked, you must replace it.
  • On the other hand, if debris is trapped under the flapper and on top of the flush valve opening, cleaning it will be sufficient to create a good seal and stop the leaking.
  • If you have a dirty flapper, clean it with running water in the bathroom sink until all debris has been removed.
  • Grab a sponge and clean the flush valve opening where the flapper sits again until it is spotless.
  • Install the flapper back and repeat the leak test. If food color or dye does not appear inside the toilet bowl after 30 minutes, then your problem is sorted.
  • As I have already mentioned, a worn-out toilet flapper will need to be replaced.

Note: Toilet flappers are not of the same size. They vary in size from 2 to 4 inches. Before buying a replacement, take time to understand what toilet flapper size you need.

  • To replace a toilet flapper, place it on top of the flush valve opening and hook its ears to the flush valve pegs. Next, connect the flapper chain to the flush handle arm.
  • It is important to make sure that you adjust the flapper chain length to just 1/4-1/2 inch slack and, importantly, perpendicular to the flush valve. If the chain is too tight, it will prevent the flapper from sealing properly, and when it is too loose, the flapper will not open fully and, therefore, a weak flush.

Note: Before buying a replacement toilet flapper, run your finger on top of the rim of the flush valve opening. It should be smooth. If it is irregular, the flapper, even if new, will not seal, and you will end up with a running toilet.

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Why Does My Toilet Still Leak After Replacing the Flapper?

As I have already mentioned, if your toilet is still leaking even after replacing the toilet flapper, you are dealing with a defective flush valve. A bad flush valve will need to be replaced.

Just like toilet flappers, flush valves are of different sizes. Again, take your time to measure yours before making the purchase.

I would recommend that as you buy a flush valve, buy a complete kit containing the flush valve, toilet flapper, tank-to-bowl gasket, and toilet tank bolts. That way, you will not need to replace any of them any time soon.

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Here is how to replace the flush valve:

1. Remove the Toilet Tank

  • Turn off the water supply to the toilet by turning the shut-off valve behind the toilet clockwise.
  • Flush the toilet and hold the flush handle down to remove as much water as possible.
  • Remove the tank lid and place it away in a safe place.
  • Use a sponge to soak the water still left at the bottom of the tank.
  • Disconnect the water supply line from the tank using your bare hands, and only use a wrench if the coupling is too tight.
  • To remove the tank, loosen the tank bolts from underneath the bowl using a wrench. If your nuts and bolts are corroded and won’t just come off, cut them off using a hacksaw blade.
  • Lift off the tank and place it on its side. Resist the temptation to place it on top of the bowl lest it falls and breaks.

2. Replace the Flush Valve

  • Slide out the tank to bowl the gasket. This gasket covers the exterior of the flush valve and prevents the toilet from leaking between the tank and bowl.
  • After removing the tank from the bowl gasket, you will see the flush valve locking nut.
  • Use slip-joint pliers to loosen and remove the locking nut.
  • With the nut out, the flush valve is now free. Disconnect the toilet flapper from the flush valve and refill the tube from the overflow tube, then take the flush valve out of the tank.
  • If you need to replace the tank bolt and washers, go ahead and remove them using a long screwdriver and a wrench.
  • Insert the new flush valve in the opening at the bottom of the tank and screw in the locking nut to secure it in place.
  • Tighten the locking nut with the slip-joint pliers.
  • Slide in the tank to the bowl gasket. The gasket should cover the entire locking nut.

3. Install the Tank

  • Lift the tank and install it on the bowl by guiding the tank bolts through the holes in the bowl.
  • Insert washers in the bolts and screw in the nuts. Tighten the bolts alternatingly to keep the tank level on top of the bowl. Do not tighten the bolts too much to prevent the toilet from cracking.
  • Connect the flapper to the flush valve and refill the tube to the overflow tube.
  • Connect the water supply line to the tank and turn on the shut-off valve.
  • Perform the leak test to be sure if the leak has stopped.

And basically, that is how to stop a leaking toilet flapper and flush valve.

If you have a leaking dual flush toilet, the flush valve seal could be the problem. I have written a separate article on how to fix that problem specifically. Read it here.