Back of Toilet Leaking and How to Fix It

A toilet may leak for a myriad of reasons. Where the leak is coming from or where the leak is will give you the first indication of the possible cause. You must inspect the problem further to find out the actual problem. Back of toilet leaking could be due to more than one reason and the severity of the leak will also vary. You may have constant leaking, dripping or leaks at specific times.

Constant Leaking

Constant leaking anywhere in a toilet implies that the locknut is not properly tightened. Whether it is the rubber washer that is inside the tank or the chip inside the porcelain surface inside the tank, there can be times when the locknuts will be loosened after periods of use. You need to tighten the locknuts and ensure they offer impeccable sealing. Do not tighten the locknuts too much so the threads don’t work or the nuts get damaged. You may also damage the tank or the base of the toilet is it is the flange where the leak comes from. The purpose is to tighten the locknut enough.

Gasket Needs Replacement

At times, it is not the locknut but some other parts or gasket. Flashing issues such as excessive rubber, improper installation or fitting, any kind of crack in the porcelain surface, cracks in valve threads and many such structural issues can cause back of toilet leaking. You will have to get the problem inspected, preferably by an experienced plumber so you can find the best solution. For serious structural problems that are beyond repair, you may have to opt for replacement.


When you don’t have a constant leak, it is mostly when you would flush it. Flushing the tank may cause leak due to a problem somewhere in the tank to the bowl gasket. You must confirm that the bowl and the tank are connected at the ridge. The ridge should have both the bowl and the tank in touch. The ridge will have wing nuts. If the tank and the bowl don’t touch the ridge, you can tighten these wing nuts so they get in physical contact. For toilets that don’t have any kind of ridge, you will notice support spacers made of rubber for stability. You can tighten the locknut of this which is usually after a triangular gasket in the tank.

Water Pressure

Check the water pressure if you have incessant leaks. Constant leak is seldom caused by increased water pressure because the pressure will subside when you have used enough water stored in your overhead tank. When the overhead tank is full or the direct lines are supplying the water into your property, the pressure of water flowing into the cistern may increase and this may cause the leak. Check the inlet valve that can contain this pressure.

Skip to content