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How to Identify & Remove a Sewer Gas Smell in Your Home

Possible Causes and Remedies to Rid Your House of the Smell

Sink pipe under wash basin
ClausAlwinVogel / Getty Images

Sewer gases backing up into your home are unpleasant and, in some cases, 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. Sewer gas smells like rotten eggs. Not all sewer gas problems are severe and need a repair expert; some are easily solved. Here are the next steps to finding the source of the smell, fixing it, and the preventive measures for keeping odors away.

Warning

Get outside for fresh air and seek immediate medical attention if you have trouble breathing, dizziness, or nausea caused by sewer gas (or any gas). A natural gas leak also smells like rotten eggs, although it has more of a skunk smell than a raw sewage smell.

Common Causes of Sewer Gas Smell

Simple, easily-fixed causes of sewer gas backing into the house are dried-out water traps, missing clean-out caps or plugs, or a failing wax ring around the toilet.

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 returning to 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 comes from a sink, run the water for a few seconds to restore the trap.
  • If the smell comes from a floor drain such as a shower drain, pour a pitcher of water down the drain to restore the proper function.

Missing Clean-out Caps or Plugs

Check the clean-out plugs or caps for the house traps or any trapped main line. Sometimes these caps or plugs fall out, break, or go missing. Clean-out plugs are access points in the main sewer lines, usually at the foundation walls, providing access for snaking out the line and removing clogs. The caps and plugs prevent gases from the clean-out line from traveling into your dwelling. If the cap or plug is broken or missing, you can buy a replacement plug at any hardware store.

Bad Wax Ring on the Toilet

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 the source of the smell, you 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 an expert 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 let pungent gases into your home. These will most typically be inside a wall or in the ceiling, requiring the help of an experienced plumber to correct this issue.

Identifying the Source of the Smell

  1. Check drains, toilets, and plumbing fixtures for signs of leaking or damage.
  2. Look for cracks or loose connections.
  3. Inspect sewer vents outside the home.

Preventive Measures

Certain factors like invasive roots growing into sewer lines or the wear and tear of time taking its toll on your plumbing systems are tough to preempt. But you can take steps to hinder sewer gases from entering your home by preventable causes.

Keep Water in All of the Traps

Plumbing traps can be found in the floor, wall, or under a sink or toilet. Figure out where they are and ensure the least-used traps keep their water level. For the seldom-used traps prone to drying out, 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 sludge-like particles can clog up the drains over time. Remove the stopper and clean out the debris with a drain snake or a do-it-yourself hook to get them clean. Flush the drain with 4 to 5 gallons of very hot (not boiling) water and replace the stopper.

If clearing the line with a small drain snake doesn't fix the problem, you may need the drain professionally snaked.

Tip

To make a DIY hook: Unbend a metal hanger into a long line, bend a small hook at the end of the wire, stick it down the drain, and pull out the debris. Repeat until you can't feel any more debris in the drain. Flush the drain with 4 to 5 gallons of very hot water.

Never use boiling water since it's unsafe for PVC pipes (if you don't know what types of pipes you have within the walls or in floor drains).

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. If you 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 usually includes hydrogen sulfide, ammonia, and methane. Hydrogen sulfide smells of decomposing organic matter and gives sewer gas the awful rotten egg smell. It's rare for high concentrations of sewer gas to back up into a home. It is more common to be exposed to higher concentrations of sewer gas in an industrial workplace.

Exposure to high concentrations of sewer gases can cause headaches, dizziness, nausea or vomiting, memory loss, poisoning, and asphyxiation. The presence of sewer gases in high amounts increases the risk of fire or an explosion.

Call a plumber right away to come to inspect your home if you cannot immediately locate the problem. Thoroughly air out your home of the odor and get outside for fresh air.

FAQ
  • Should you leave your house if you smell sewer gas?

    If you smell sewer gas, you should open the windows and go outside into the fresh air.

  • What are the symptoms of sewer gas poisoning?

    According to health departments, exposure to sewer gas at high levels can result in serious symptoms. If you experience trouble breathing, extreme fatigue, dizziness, nausea, or other abnormal symptoms, seek medical attention immediately.

  • Is sewer gas an emergency?

    Sewer gas can lead to ill health effects even if the exposure is small over a long period of time. It should be addressed as promptly as possible. If you're experiencing symptoms, seek emergency medical attention.

  • How do you test air for sewer gas?

    You can test the air for sewer gas using a gas leak detector. Another option is to call a plumber for a smoke test to source the leak.

The Spruce uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  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.