Sewer Smell in the House: Causes, Checks and Fixes

Drains are designed to keep sewer gas out of the house. When you smell it, one of those protections has failed somewhere.

Common sources

Source	Clue	Fix
Dry P-trap	Unused sink, shower or floor drain	Run water to refill the trap
Failed toilet wax ring	Smell near the toilet base; rocking toilet	Replace the wax ring
Blocked roof vent	Gurgling drains and smell	Clear the vent stack
Loose or missing cleanout cap	Smell in basement or utility area	Tighten or replace the cap
Cracked drain or vent pipe	Smell inside a wall or basement	Repair the pipe
Sink overflow hole	Smell at a bathroom sink	Clean the overflow channel

Start here

Run water for a minute in every sink, tub, shower and floor drain, especially rarely used ones.
Check each toilet for rocking or water at the base.
Look for cleanout caps in the basement, crawl space or garage.
Notice where the smell is strongest and whether it comes and goes with rain, wind or drain use.

Is sewer gas dangerous?

Sewer gas can contain hydrogen sulfide and methane. Small amounts are mostly unpleasant, but strong or persistent smells should be fixed promptly. If you ever smell something like natural gas instead, leave and call the gas utility.

When to call a plumber

If the easy fixes do not work, a plumber can run a smoke test, which pushes harmless smoke into the drain system to reveal leaks, or inspect the sewer line with a camera. See our sewer camera inspection cost guide.

Smell by location

Where you smell it	Check first
Bathroom, near the toilet	Wax ring, loose toilet
Bathroom sink	Dry trap, overflow channel buildup
Basement	Floor drain trap, cleanout caps, cracked cast iron
Laundry room	Washer standpipe trap
Throughout the house	Blocked vent or main line problem
Outside near the house	Vent stack, septic system or sewer line

What a smoke test involves

A plumber seals the drain system and blows harmless, non-toxic smoke into it, often through the roof vent or a cleanout. Wherever the system leaks, smoke appears: at a loose fitting behind a wall, a failed wax ring or a cracked pipe. It is one of the fastest ways to find a hidden source.

Common questions

Why does my house smell like sewage only sometimes?

Changing air pressure, wind across the roof vent or drains being used can push gas through a weak spot intermittently.

Can a dry P-trap cause a sewer smell?

Yes. It is one of the most common causes, especially with guest bathrooms and basement floor drains.