How to Replace the Rubber Seal at the Back of the Toilet?

Written by

Paulk Webb


Freddie J. Hagopian

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how to replace rubber seal at back of toilet

A toilet leak is a nuisance but a common and solvable problem. Its occurrence has varying causes, but if the leak is at the bottom of your tank, the culprit is most likely the toilet rubber gasket.

The rubber seal ring can be damaged and age over time, hence the failure to stop water from coming out. Luckily, this article will teach you how to replace rubber seal at back of toilet with ease.

What is a Toilet Rubber Seal?


The tank-to-bowl gasket is the rubber piece in the toilet that connects the tank and the bowl with a water seal tightness. This enables the flushing mechanism to operate without water spilling onto the floor.

Through time, the material deteriorates like the rest of the toilet’s parts. However, hard water can wear out the toilet tank rubber seal faster because of the minerals eating away at the material through repeated exposure. In short, hard water can corrode rubber.

Instructions for Toilet Seal Replacement

What to prepare:

  • sponge or towel
  • flat screwdriver
  • wrench
  • tank-to-bowl gasket kit

Step 1: Initial Preparation

Before you change a toilet seal, you have to ensure that no water will come into the tank and that it is wiped dry.

  1. Turn or pull the shut-off valve to cut off your water supply. Then flush the toilet to drain the tank so that its water won’t leave a mess on your floor.
  2. If there’s still water left in the tank, grab a sponge or towel to absorb it. If you have a wet vacuum, you can utilize it as well.
  3. Disconnect the water supply hose from the tank by turning the nut counterclockwise (or clockwise if it doesn’t work).

Step 2: Disconnect the Tank From the Bowl

1. Use a flat screwdriver to unscrew the bolts’ heads from inside the tank.


2. The said bolts go outside the tank as well. Use a wrench to unscrew their lock nuts.


3. After unscrewing the bolts, hold both sides of the tank tightly and lift it to disconnect it from the bowl.


4. Lay the tank on a towel and proceed to remove the old toilet flush rubber seal in the next step.

Step 3: Replace the Seal on Toilet Outlet Pipe

The tank-to-bowl gasket kit will come with all the necessary materials that you need to replace a toilet seal. Still, ensure that the new gasket is the right size by comparing its diameter with your current gasket!

1. First, remove the old toilet seal from under the tank.


2. Put the new gasket on the plastic nut of the tank and make sure that it covers the entire nut. The new gasket will seem smaller and tighter than the older one, which is normal.


3. Take the bolts and washers from the kit and arrange them like this: rubber washer > metal washer > bolt. The rubber washer is the one that touches the tank from the inside.


After arranging them correctly, insert the bolts into the tank’s holes.

4. Going under the tank, the washers and nuts should be inserted into the screw in this order: rubber washer > metal washer > lock nut


5. With the wrench, tighten the lock nut under the tank in place. You can also use a flat screwdriver to hold the bolt steady from inside the tank while wrenching the lock nut tight.


Step 4: Connecting the Tank Back to the Bowl

1. Gently lift the tank and insert its screws into the bowl’s holes.


2. Take the washers and nuts, then follow the same order as before under the tank: rubber washer > metal washer > lock nut


3. Tighten the lock nut with a wrench just enough to secure it. Do not overtighten or it will crack the porcelain.


4. Connect the water supply hose back into the tank.


How Do I Replace the Rubber Seal for RV Toilet?

While RV toilets don’t have tanks similar to residential toilets, they still have seals that separate the bowl from the waste tank or cassette below. Before anything else, always remember to turn the shut-off valve or water supply off first!

  • Depending on the type of RV toilet, you can simply take the seal out while wearing gloves, since it’s usually visible when you open the bowl’s cover.


You’d have to install the new gasket through the same hole as well.


  • In other cases, you have to remove the RV toilet bowl to see the seal and replace it. You can also use plumber’s grease and rub it on the new seal to secure it in place.


Frequently Asked Questions

Why Is My Toilet Leaking From the Back?

There are several reasons why your toilet may leak from the back, which are listed below:

  • your toilet float is higher than recommended;
  • your flapper is worn out;
  • you need a toilet flush valve seal replacement (or new flush valve gasket);
  • your toilet tank has cracks

How Do I Know if My Toilet Seal Is Leaking?

To know if your tank-to-bowl gasket is causing leaks, see if there are wet areas below your toilet tank, toilet base, and the floor. You can also check the bolts in the tank and see if they are damaged or loose.


The tank-to-bowl gasket is an important accessory to keep water from spilling from the tank. That’s why you need to know how to replace rubber seal at back of toilet to avoid or stop leaks.

Begin by turning off the shut-off valve and draining the tank. After this, you can safely disconnect the tank from the bowl and remove the old gasket hardware to install the new one. Then, reconnect the tank to the bowl by securing the washers and lock nuts.

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