How to Identify and Remove a Sewer Gas Smell in Your House

Possible Causes and Remedies to Rid Your House of the Smell

Sink pipe under wash basin
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Sewer gases backing up into your home can be a severe problem. Sewer gas is a generic term for the noxious mix of chemicals that are the by-product of decaying waste. You'll know you have a sewer gas problem if you smell the distinct odor of rotten eggs in your home. Not all gas backups are so serious, and some are quite easily solved. So how do you know if you need an urgent repair?

Common Causes of Sewer Gas Smell

There are some pretty normal reasons why you may smell sewer gas in parts of your house that are easily fixed.

Water Traps

Water traps, sometimes called P-traps or S-traps, are commonly located near floor drains and laundry tubs and are underneath every sink in the house. They work by trapping water inside the curve and blocking the gas from traveling back into the house. Traps dry out when they haven't been used much, the air in the house is very dry, or there is a leak somewhere before the trap. If the trap is dried out, the sewer gas has a clear path into the house. Here are two solutions:

  • If the smell is coming from a sink, simply run the water for a few seconds to restore the trap.
  • If the smell is coming from a floor drain, pour a pitcher of water down the drain to restore the proper function.

Missing Clean-out Plug

Check the clean-out plugs for the house traps or any trapped main line. Clean-out plugs are access points in the main sewer lines, usually at the foundation walls. They provide access to snake out the line and prevent gases from traveling into your dwelling. Clean-out lines are places for easy removal of clogs. The lines are capped so sewer gas cannot escape into the house. If one or more of these caps are missing or broken, this can be the culprit of the smell. You can buy a replacement plug at any hardware store.

Bad Wax Ring on the Toilet

In between the toilet flange and the base of the toilet, there should be a wax ring to provide a watertight and airtight seal. This wax ring can occasionally leak or become compromised, letting sewer gas into the home. If that's your cause, you'll need to replace the wax ring on the toilet.

More Serious Repairs

Other causes of the smell are not so simple and will require more extensive, more expensive repairs.

Sewer or Septic Pipe Leaks

Sewer and septic line leaks are harder to diagnose and require more expertise to repair. If your toilet is gurgling and your drains are slow in addition to the sewer gas odor, you probably have a sewer line leak.

Loose Connections

Loose connections along the vent pipe or sewer line can also let pungent gases into your home. These will most typically be inside a wall or in the ceiling, so you'll need the help of an experienced plumber to correct this issue.

Preventative Measures

While you can't do anything about roots going through sewer lines or the wear and tear of time taking its toll on your plumbing systems, there are some steps to take to prevent the sewer gas issue from returning to your home.

Keep Water in All of the Traps

Confirm the location of all of the plumbing traps in your home, whether they are in the floor, wall, or under a sink or toilet, and make sure the least-used traps keep their water level. For the traps that are seldom used and prone to drying out, you can pour a couple of tablespoons of vegetable oil on top of the water to help slow evaporation.

Clean out Your Drains

It happens in every house—debris, hair, toys, and all manner of particles can clog up the drains over time. To get them clean, remove the stopper and clean the debris off of it. Set it aside. Bend a small hook at the end of a wire, stick it down the drain, pull out the debris, and throw it in the trash. Repeat until you can't feel any more debris in the drain. Flush the drain with 4 to 5 gallons of very hot (not boiling) water and replace the stopper.


The drain line will be much longer than the wire. If clearing the line with a wire or small drain snake doesn't fix the problem, you may need the drain professionally snaked.

Keep the Vent Stack Free From Debris

The vent stack is the pipe that sticks out of your roof. It should be kept free of clogs and debris. Unless you have trees with branches that hang directly over the vent stack, you likely will not have to deal with clearing the stack. If you do have trees or other features that could drop debris on the vent stack, hire a professional to do semi-regular cleanings.

Is Sewer Gas Dangerous?

Sewer gas can include hydrogen sulfide, ammonia, and methane. The hydrogen sulfide is what gives sewer gas that awful rotten egg smell. It is rare to become exposed to high concentrations of sewer gas in a home. However it is more common to be exposed to higher concentrations of sewer gas in an industrial workplace. Exposure to high concentrations of these gases can cause symptoms, including headaches, dizziness, nausea or vomiting, memory loss, poisoning, and asphyxiation. In large enough amounts, there is even risk of fire or explosion.

Call a plumber right away to come inspect your home if you cannot immediately locate the problem. Then thoroughly air out your home of the odor and get outside for fresh air. Your body will also quickly and naturally excrete lower levels of the hydrogen sulfide through bodily fluids.


If you smell sewer gas and experience trouble breathing, dizziness, or nausea, seek immediate medical attention.

Article Sources
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  1. Illinois Administrative Code. Section 890.410 Fixture Traps/Continuous Waste. Illinois General Assembly Public Health.

  2. Sewer Gas. Wisconsin Department of Health Services

  3. Prevent Sewer Gas Backup. North Dakota State University

  4. Sewer Gas. Wisconsin Department of Health Services