A washing machine smells like sewage because of mold and bacteria buildup or a clogged or dry drain. Run a hot cleaning cycle and clean the gasket.
Common causes
- Mold and bacteria in the drum or gasket.
- Clogged drain or standpipe.
- Dry P-trap.
- Detergent buildup.
- Sewer gas backing up.
Fix
- Run a hot cycle with a washing machine cleaner or 2 cups of white vinegar then 1/2 cup baking soda.
- Wipe the door gasket.
- Leave the door open.
- Clean the drain.
Prevention
Use less detergent.
Call a plumber
If the smell persists.
Where the sewer odor comes from
A sewer smell from a washer usually results from a dry or blocked P-trap in the standpipe, biofilm in the drum or gasket, or a venting problem. The standpipe should hold water in the U-bend, which blocks sewer gas (hydrogen sulfide and methane) from entering the room. Front-loaders trap water in the rubber door seal where mold grows.
- Standard drain trap height for washers is typically between 18 and 30 inches above the trap weir under many plumbing codes.
- Low-temperature washes and excess detergent leave residue that feeds bacteria.
- A clogged drain line lets water sit and rot.
Fix and prevention
Run a hot cycle (60 C or 140 F) with a washing machine cleaner or 2 cups of white vinegar followed by a second cycle with 1/2 cup baking soda. Wipe the gasket and leave the door ajar between loads. Pour a quart of water into an unused standpipe to refill the trap. Use high-efficiency detergent in the recommended amount only. Call a plumber if odor persists or if drains gurgle, which may indicate a vent or main line blockage.
Why the odor appears
A sewer smell in a washer comes from bacteria and biofilm in the drum, gasket and drain, or from a dry drain trap letting sewer gas in. Low temperature washes and high efficiency detergent buildup contribute.
Fix
Run a hot cycle with washing machine cleaner or white vinegar, clean the gasket, leave the door open after use, and check that the standpipe trap is filled. A plumber can fix venting problems.
Sources of sewer gas
Washers drain into a standpipe with a P-trap holding water that blocks sewer gas. If the trap dries out, is missing, or the vent is blocked, odor rises. Biofilm in the rubber door seal of front loaders also smells like sewage. Hydrogen sulfide, a rotten egg gas, comes from sulfur reducing bacteria.
Cleaning and repair
Clean the gasket with diluted bleach or vinegar, leave the door open, run a monthly tub clean cycle at 140 F (60 C) and use high efficiency detergent in the right amount. Pour a quart of water down the standpipe. If odor persists, call a plumber to check the vent and trap. Sewer gas at high concentrations is hazardous.
Based on data from Consumer Reports and the American Cleaning Institute
