Finding and Fixing Toilet Leak

Yes, it is true that toilets are one of the most common source of leaks in an average household.  And yes, toilets are not as complex as other plumbing fixtures or appliances; but, this does not mean that you can automatically assume that leaks are caused by a bad flapper, or worn out seals.

How will you know how to find and fix toilet leaks?

Tank Sweating

When looking for something (including leaks) sometimes the best solution is to know where to start.  A condition known as tank sweating happens when the temperature inside the toilet tank is colder than the temperature outside.  This causes the water to condense and drip to the floor.

This condition is more prevalent during the warm summer months but can happen in any season.  The way to deal with this is to use tank liners that will insulate the water inside the toilet tank.

There are also anti-sweat toilet tank valves that mixes cold and warm water in the tank to reduce the temperature difference.

To confirm whether it is tank sweating you have to wipe the outside of the toilet tank and visually observe if condensation is happening.

Tank Leak

Another possibility is to check if there is a leak from inside the toilet tank.  Add a few drops of food coloring to the water in the toilet tank.  Instead of flushing, wait for the food coloring to settle.

In about 15 minutes try to observe if some of the colored water is dripping on the floor.  This would confirm that there is a toilet tank leak.  Where is it coming from?

The most obvious source of the leak would be a crack on the tank.  Try to look for any discolored portion of the tank or an area outside the toilet tank that is highlighted with colored water.  This would usually be an indication where the actual leak is coming from.  How do you fix the leak? Try these following tips from south bay plumbing.

  • Between the Tank and the Bowl – if the colored water drips from the area between the tank and the bowl, the probability is that the bowl gasket must be replaced along with the tank-to-bowl bolt washers. The more you flush, the more leaking will happen.  The tinted water may also appear near the edge of the bowl not only along the center.  This happens when the bowl design has a lower side near the front instead of the inlet hole.  To fix this problem you have to replace the gasket and the washers, which are available from most plumbing stores.
  • Fill Valve Shank Gasket – the fill valve is attached to the tank and allows water to get into the tank. The shank gasket inside the tank is connected to the fill valve.  The colored water will reveal if the leak is anywhere in this portion.  It will also be easier to see the presence of cracks within the area of the gasket.  Tightening the nut with a quarter turn should stop the toilet leak; otherwise replace the gasket.
  • Refill Tube – when the source of the leak seems to be from the back of the tank near the top, the possibility is that it has something to do with the refill tube or it might have come loose. Simply make sure that the refill tube is firmly connected.
  • Cracked tank – if the problem is really cracks on the porcelain tank, the only solution is to replace the toilet tank and have a new one installed by a professional.

Other Sources of Leaks


Aside from the toilet tank, there are other parts of the toilet plumbing system that can cause leaks.  These are the:

  • Shutoff Valve – a busted valve can allow water to seep from the pipe and even leave moisture behind the wall. Valves are not repaired, they must be replaced.
  • Supply Line – leaks can happen at either end of the supply line. When this happens, replace it with one made of flexible stainless steel that are easier to attach, but durable.
  • Wax Ring – found under the toilet, it can allow wastewater to seep back into the bathroom. You may notice water coming from under the toilet every time you flush if the wax ring is worn out.  What you have to do is to reseal the toilet with a new wax ring and even change the caulking around the toilet base as well for good measure.
  • Other part of the bathroom – sometimes leaks coming from the shower, sink, or tub tend to accumulate near the toilet only because it is the lowest fixture inside your bathroom. This means that the problem lies elsewhere.

You now have a fairly good idea how to find and fix toilet leaks.  A good rule of thumb is that if you are unsure, call for professional help!