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How to Diagnose a Bad Toilet Trap: Complete Guide

Any leak, particularly in a combined toilet and bathroom setup, can sometimes be challenging to detect. It’s an area in your house that often gets wet, especially when several people are bathing or showering daily.

Here are the things you need to check for a bad toilet trap:

  1. Check for water running on the floor
  2. Check for foul-smelling odor and discoloration of the surrounding tiles
  3. Check for leaks on floors or ceilings in your bathroom
  4. Check for water running out of your overflow pipe when you flush

A trap is an integral part of the toilet flushing mechanism. Consisting of a wax ring or rubber seal and flange, it is constantly exposed to water and some movement and is, therefore, susceptible to wear and tear and may eventually leak with time.

Failing to detect and diagnose or act on a leaking toilet trap can lead to toxic pools of sewerage accumulating in the bathroom, exposing you and your loved ones to harmful bacteria which could cause illness. A leaking toilet trap can also cause a  foul odor and unsightly stains that will build up on your bathroom floor.

Toilets: The Basic Components

Water pooling on your bathroom floor is a telltale sign that somewhere, a pipe or seal has sprung a leak. But before jumping to any conclusions, it is essential to understand how a toilet works to correctly identify the source of your leak.

Residential tank-style toilets have several working parts that operate sequentially every time a toilet is flushed. Here are the main components and their primary function.

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The Tank 

The tank is usually located behind and above the toilet bowl and seat. The container for the water rushes into the bowl when you flush the handle and forces the waste products into your sewerage pipes and away from your house.

Inside the tank, several vital components facilitate the entire process, including the float arm and ball, ball-cock, refill tube, overflow tube, and others.

The Bowl 

The bowl is the open area inside the pan where the waste and water from the tank go and has a hinged seat fastened on top for the user to sit on. 

The rim underside of the bowl receives the flushing water from the tank channeled in by gravitational pull concentrated towards the water reservoir at the bottom of the bowl.

The Trap

The trap (or siphon) is the part of the toilet pan that channels the wastewater out into your drainage system. It is designed for the same purpose as any standard kitchen or bathroom drain to trapping clean water in the curved part of the outlet pipe to separate the inside drain from the rest of the outside drainage system.

This creates a barrier designed to keep unwanted sewer gas odors from permeating the inside of the house or dwelling.

There are two types, the S-Type, which is fastened to the floor behind the toilet pan, and the P-Type connected to the wall behind the toilet pan. The S-Type flushes vertically, and the P-Type flushes horizontally.

NOTE: The type of trap used is dependent on the construction of the dwelling and the drainage system architecture used. The S-Type is the most commonly found installation type.

Between the Trap end and the outlet drain pipe, a wax ring or rubber seal is installed over the drain closet bend to hermetically seal the drainage outlet mechanism and facilitate a proper flushing action and prevent any leaks.

Detecting a Leak: Finding the Source

So the bathroom has not been used for a few hours, but you discover a wet patch on the floor around the toilet. It can only be one of a few things, right, but which is it?

  • The water supply line or valve is dripping. Water is pooling around the water inlet faucet.
  • The connection between the tank and the pan. Water is usually found behind the toilet pan under the tank.
  • A cracked toilet pan. The porcelain itself is cracked and leaking.
  • A failed wax ring. This is the most common problem found, causing the trap to leak.
If you find water on the bathroom floor around the toilet’s base, chances are it’s the trap’s wax seal and flange that are leaking.

This leak is often accompanied by a foul-smelling odor and discoloration of the surrounding tiles, especially if the leak has been occurring for some time.

The best way to conclusively prove the trap seal leaking is to eliminate all the other possibilities. To do this, you have to do the following:

1. Close All the Faucets and Water Valves

Make sure your toilet tank is filled up ready for flushing, then close all the faucets in the bathroom, including the water supply to the toilet. This faucet or valve is usually located behind the pan under the tank with a meshed pipe leading to the underside of the tank.

2. Wipe the Bathroom Floor Dry

Take a towel or large cloth and wipe the floor around the toilet dry. It must be completely dry, or you may get confused by water from a different unrelated source.

3. Flush the Toilet

Once the water supply is cut off and the entire area around the toilet basin is bone dry, flush the toilet and wait to see if water pools around the toilet’s base. If necessary, you may add some food dye to the flushing water in the bowl to aid you in seeing the water leak more effectively.

4. Inspect the Floor for Water Leaks

Check the base around the toilet, especially at the back where the trap connects to the flange under the floor, for any signs of water or building moisture. If the leak is minimal, you may need to repeat the process by filling up the tank and bowl and flushing a second time.

5. Mop Up the Remaining Water

Disconnect the water inlet pipe from the bottom of the tank. Take a towel and dry the inside of the tank, taking care not to bend or break any of the plastic components inside the tank.

TIP: If you still have residual water inside the bowl, you can use a solidifying gel such as Oatey Liquilock to prevent any water spillage after removing the toilet pan. Just pour it into the bowl and wait a few minutes for the water to form a solid gel.

6. Remove the Toilet

There are usually two bolts on either side of the pan that secures the toilet basin to the floor. Remove the caps and unscrew the bolts. Lift the entire toilet mechanism off the ground and set it aside. You may need someone to assist in this step as the toilet can be pretty heavy.

7. Inspect the Wax Ring

This is the part where the truth will be revealed. It is usually quite evident when the flange and ring are exposed that the toilet is leaking. Ensure you are wearing protective rubber gloves to avoid coming into contact with any sewage remnants. Stick a cloth into the hole to prevent the sewer gases from escaping to avoid debris falling in.

8. Scrape Off the Old Wax

Taking a disposable scraper, remove all the wax and discard immediately, including the scraper used. Check that the flange bolts (that connect the toilet bowl to the floor) are tight and in good condition. The flange itself should be in good condition, free of rust, tight-fitting.

9. Insert the New Wax Ring or Seal

There is usually more than one wax ring option available. Use an extra thick one if the flange is recessed. There are also more modern non-wax seals like this one on Amazon that’s easy to install and seals on uneven floors or over tile floors with recessed flanges but without the mess.

Follow any installation instructions on the packaging or consult with an expert if you are unsure.

10. Replace the Toilet Pan

Now that your seal and flange have been checked and replaced, it is time to secure the toilet back in its place. Align the bowl holes with the flange bolts and press them down into the wax o-ring seal. Sit on the toilet and push down to create a watertight seal.


The cursory steps shown here for basic leak detection should be easy enough for anyone suspecting a leaking toilet. You do not have to be a DIY expert. If you are comfortable proceeding once the leak has been discovered, this will save you a few bucks. If you are unsure or lack sufficient skills or confidence, it is advisable to consult with a professional plumber.