It seems as if the seal at the bottom of the tank is no longer perfectly planar. It is slowly leaking until the flotation device is low enough to trigger refilling.

bottom of the tank

I am guessing that this can be fixed by replacing just the part that rotates (name?), and that it is not necessary to replace the entire mechanism.

  1. Is this accurate? In particular, could the leak be the result of the bottom part of the seal becoming crooked, which would be a lot more complicated to replace?
  2. Does the rotating part come in a standard size or in one of a variety of few sizes? Does this picture tell you what I should be asking for at the hardware store?


Assuming that the "flapper" (credit for naming it: Michael Karas) is the part attached to the hinge, I noticed that the flapper has another seal attached to it. The seal is made of silicone and is the soft material that stops the water. Is the seal a replaceable part on its own? Alternatively, I do not see which movement will detach the hinge. The material for the axis (as you see in the picutre) is a very thin tube of plastic. Breaking it would mean that a trivial repair would all of a sudden become a serious one.

  • Measure the diameter of the flapper valve across the middle parallel to the axis of rotation. If you get about 3.75 in, this is a 3-inch. Note the make and model of the toilet tank (usually stamped inside the tank) and take this and the picture into Home Depot or Lowes. Feb 18, 2018 at 17:21
  • I think if you go buy a new flapper it will be obvious how it attaches. You are correct if you were to break off the hinge posts you would then need to replace the whole seat assembly which requires removing the tank. It should snap off so easy its not an issue though.
    – agentp
    Mar 4, 2018 at 19:15
  • By the way i'd recommend making sure you can turn off the water supply (valve behind the toilet). You can swap the flapper without turning the water off, but you want to be sure the valve isn't frozen in case you run into problems.
    – agentp
    Mar 4, 2018 at 19:18
  • @agentp Thanks for the advice. Two surprises: 1- the valve is indeed stuck (=frozen?), and 2- the hand is made of plastic, so I can't apply even a bit of torque to dislodge it. Suggestions very welcome. I'm guessing the next one up is to shut down the water to the house.
    – Calaf
    Mar 4, 2018 at 19:46
  • The arms are plastic, but notched out at the bottom, so they snap on and off the pivots. Just pull up on one side at a time and it will pop off. Before installing the replacement, wipe off the rim that it sits against. Run you finger around it to see if there are any irregularities. It should be completely smooth and continuous for a good seal. BTW, the replacement flappers typically come with a collar with pivots that you can use if you somehow break off the original pivot arms. Just smooth off anything still sticking out from the stand pipe. I've never seen the pivots break off, though.
    – fixer1234
    Mar 4, 2018 at 22:10

2 Answers 2


The part that you most likely need to replace is known as the flapper. It is the part shown in your picture that has the hinge arms that go back to the posts on the sides of the stand pipe. The flush lever also connects to this flapper to pull it up when the toilet is flushed.

The flappers are made of a flexible rubber or silicone material. Water treatments like chlorine in the water will degrade the flexibility of the flapper over time. This can lead to cracking or hardening of the flapper and can allow for the type of slow leak like you describe.

I find that I have to replace the ones in my house about once each 2 years or so. Note that there are some types that are better than others so look carefully at the options that you find at the home center or hardware store. Some of the replacement parts are designed to be "universal" and can be adapted to the several different hinge styles used in the water closet of the toilet. The ones I purchase generally have to have part of the thing cut away to adapt it to my usage.

Take your picture with you to the store. It will help you pick out just what you need.


Most flappers at the hardware store are made from one piece, in a soft material, probably rubber, but possibly silicone.

If the flapper is rigid, it will be made from two parts. In addition to the rotating part (pictured in the question), there is also a silicone ring.

Although the axis looks like a cylinder from distance, its cross section is actually oval. You can determine this because it is possible to remove the flapper after turning the flapper slightly. It is not easy to remove it in either the bottom (closed) or the fully open positions, but it is fairly easy to pull it out when it's halfway without using force that could risk breaking the two axes on either side.

If you're lucky, you'll find some yellowish dirt in one part of the opening at the bottom of the tank. This just needs to be cleaned (cause of yellow deposit?). If you're doubly lucky, no new part is necessary, the silicone seal will just have some blisters from the yellow deposits. It wouldn't do to remove the blisters, but it's easy to flip the seal over and use the other side for a proper seal.

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