The short answer
Common Causes
The most common cause is a clogged or improperly vented washing machine drain line. When water can't flow freely, sewage gases back up into the room. Another frequent culprit is a dry P-trap in a floor drain, which allows sewer gas to rise up when the trap hasn't held water for a while.
A leaking waste pipe behind the washer can also produce a sewage odor, especially if the leak is slow and hidden. Additionally, the washing machine itself can harbor bacteria and mold in the drum or filter, creating a musty, sewer-like smell over time. Check these areas first.
- Clogged or blocked drain hose
- Dry P-trap in floor drain
- Leaking waste pipe behind washer
- Dirty or clogged washer filter
- Buildup of detergent and fabric softener
- Improper venting of drain line
Check the Drain Hose
Pull the washing machine away from the wall and examine the drain hose. Look for kinks, clogs, or a hose that is pushed too far into the standpipe, which can cause siphoning and poor drainage. If the hose is damaged or cracked, replace it.
Also verify that the standpipe height is correct, typically between 18 and 30 inches. Too low allows siphoning, too high can cause standing water and odor. If the hose is old or brittle, a simple replacement often solves the problem.
Inspect the Floor Drain
Many laundry rooms have a floor drain that connects to the sewer. If this drain is rarely used, the water in the P-trap can evaporate, letting sewer gas escape. Pour a gallon of water down the drain to refill the trap and see if the smell disappears.
If the smell persists, the floor drain may be clogged or the trap may be cracked. You can try cleaning the drain with a mixture of baking soda and vinegar, but if the odor remains, it might be time to have a plumber inspect the drain line.
- Pour water down the floor drain weekly
- Check for cracks in the P-trap
- Clean the drain cover and area
- Use a drain cleaner if needed
Clean the Washer
Front-loading washers are prone to mold and mildew buildup in the rubber gasket and detergent drawer. This can create a foul smell that resembles sewage. Run an empty hot water cycle with a washing machine cleaner or a cup of white vinegar to kill the bacteria.
Also clean the filter located at the bottom front of the machine. Debris and lint can accumulate there, causing odors. Remove the filter, rinse it thoroughly, and replace it. Doing this every few months helps prevent smells from returning.
When to Call the Pros
If you have checked the drain hose, floor drain, and washer, and the smell persists, the issue may be deeper in your plumbing, such as a blocked vent pipe or a broken sewer line. These problems require specialized equipment to diagnose and fix.
Local water damage pros can also inspect for hidden leaks behind walls or under the floor, which might be causing the odor. They have moisture detection tools to find the source of the problem and can advise on the next steps for repair.
- Persistent odor after basic checks
- Visible water damage or staining
- Signs of a sewer line backup
- Multiple drains in the home smell
Need help right now?
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Call Now (425) 407-5186Frequently asked questions
Why does my laundry room smell like sewage only when I run the washer?
This usually indicates a drain line issue, such as a partial clog or improper venting. When the washer pumps out water, the backup pushes sewer gas into the room. Check the drain hose for kinks or blockages and ensure the standpipe is the correct height.
Can a sewage smell in the laundry room be a health hazard?
Sewage gas contains methane and hydrogen sulfide, which can be harmful in high concentrations. Low levels can cause headaches or nausea. If you feel unwell, open windows and leave the area. See a doctor if symptoms persist. Address the source promptly.
Will my insurance cover the cost of fixing a sewage smell?
Policies vary, and your insurer decides what is covered. Generally, damage from a sudden sewer backup might be covered, but gradual leaks or maintenance issues are not. Check your policy and consider adding sewer backup coverage if available.