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7 Common Reasons for a Sewer Odor - How to Find and Resolve

sewer odorExperiencing a mystery odor? Need to track down the source? Use this as your guide to identify and resolve odor in your home…

Locating reasons of a sewer odor is an arduous task. Here at Legendary Home Services, we have come across many different sources of pungency.

Because we love to help people identify and remedy their issues, we have created a list to accompany your investigation.

Below are the 7 most common causes of mystery odors:

Fixtures with limited use:

Bathtub or sink drains that are rarely used can allow sewer gas to seep into your home. The p-trap under the drain opening is designed to hold water, blocking those gasses. If a drain is rarely or never used, this allows the water to evaporate and let the sewer gas into your home through the drain opening. It is important to run water down these types of pipes a few times per month to keep water in the p-trap.


Drain Openings:

When build-up or soap scum collects in the opening of the drain, it creates a prime area for bacteria to thrive. Multiple applications of enzymes and drain chemicals can resolve the matter. Often, when attempting to remove an odor in the shower drain, people will only try the application one time. Use your cleaning product of choice multiple times each day over the period of a week.

sink drain build up

Mildew and Stagnant Water:

Some odors come directly from the shower itself. Check your shower thoroughly for areas where water may hide. Stagnant water supports bacteria, which releases odors. Examine the shower doors for areas that may conceal water. The metal tracks that support the doors lose their seal as time passes. Water can then become trapped in areas where it cannot evaporate, growing bacteria and enabling unpleasant odors to be released. To address this, you can seal the shower doors with silicone. Be sure to clean any visible mildew before applying the silicone.

shower doors


Your toilet can provide two different sources of foul odor.

  1. Bad seals from the wax gasket (under the toilet) allow sewer gas to permeate from under the toilet

The wax ring used to seal the drain and prevent water leakage is designed not to degrade. However, if the toilet bowl becomes loose, the wax ring loses its seal. Check your toilet for stability. If you believe the wax gasket has been impacted, replacing it will be prudent.

check the toilet for movement

  1. Inspect the base of your toilet bowl. Does it have a clean, complete seal? The base of your toilet should be caulked to the floor. When the caulking is not present, water and urine can leak under the toilet and enable bacteria to grow. Apply some tub and tile caulk around the base. A well-sealed toilet will safeguard from lurking aroma.

toilet base with caulk seal

Sink Overflow:

This portion of the sink is usually unnoticed. When odors emerge, the overflow is frequently the culprit. The sink overflow can accumulate build-up and soap scum over extended periods of time. Clean the overflow with a thin brush. Applying drain cleaning chemicals is also a good idea to help remove debris the brush is unable to reach.

sink overflowUnderside of the Garbage Disposal Rubber Guard:

The black rubber splash guard at the entrance to the garbage disposal can be a common cause of foul odors. Cleaning the underside of this splash guard is key to cleaning the disposal. Using a thick cloth, with the splash guard turned inside out, scrub away any accumulated food. After cleaning, run hot water and activate the disposal. While it is on and the hot water is running, add soap to the disposal and allow to run for 30 seconds. This process will assist in cleaning any leftover debris.

disposal splash guard

Drain and Sewer Clean-Out Covers

The cover plates that hide clean-out caps in the wall are attached to the cap with a screw, which degrades over time. When this happens, sewer gas can seep into the home. Located near toilets, under sinks, and behind fixtures, check the cover plates and replace the screws as needed with new ones. Use thread sealant tape on the threads of the new screw.

clean out screw

If these issues have all been addressed and the odor continues, you may want to consider calling a professional plumber to evaluate. A skilled worker can check the most elaborate systems in your home, such as:

Drain Vent Pipes

Broken vent pipes can discharge sewer gas. These vents are located behind the walls and are difficult to inspect without a sewer camera. A professional can check vents by conducting a camera inspection.

Quality of your incoming water supply:

A water quality test can determine if high levels of sulfur and chlorine exist in your water. Vapors from a potable water supply can release aromas that people associate with sewer odors.

Backdraft from Septic Tanks

Back drafting is not common but can cause a real issue. Specialized equipment can be used to check for this problem.