Before you assume the worst, know this: most sewage smells inside a home come from one of two causes, and both are easy fixes. It's very rarely a main sewer line problem — though when it is, you want to know quickly.
Here's how to work through it.
Start with the easy one: run water in every drain
Every drain in your house — every sink, tub, shower, floor drain, and the little drain inside your washing machine pan — has a p-trap, the curved section of pipe directly below the fixture. The trap holds water that creates a seal against sewer gas from the drain system.
If a drain isn't used for weeks, the water in its trap evaporates. Sewer gas then flows freely up through that drain into your home.
The test: Walk through the house and run water for 30 seconds in every single drain, including ones you rarely use — the guest bathroom sink, the basement utility sink, the floor drain in the laundry room. For toilets, just flush. This refills any evaporated traps.
Wait a few hours and see if the smell is gone. If it is — that was your cause. It's free to fix and mostly preventable by running those rarely-used fixtures once a month.
Cause #2: failed toilet wax ring
If the smell is concentrated near a specific toilet — especially a bathroom you've noticed smelling right after a shower or a flush — the toilet's wax ring seal is likely the culprit.
The wax ring sits between the base of the toilet and the drain flange in the floor. Over time (or after a toilet shift), it can fail. When it does, sewer gas seeps up around the base of the toilet into the bathroom.
How to tell:
- Smell is worst in one specific bathroom
- Smell is stronger after a shower (humid air pushes the gas up)
- Toilet rocks slightly when you push on it
- Water staining at the base of the toilet (sign of a minor water leak too)
Fix: Replace the wax ring. A plumber can do this in 30 minutes on a service call. Part cost is under $10; the work is in lifting and re-setting the toilet.
Cause #3: vent pipe issue
Your plumbing drain system has vertical vent pipes that extend through the roof. These let sewer gas escape outside rather than building pressure in your pipes. If a vent pipe is blocked (bird nest, leaves, ice) or damaged, sewer gas can come up through drains even when traps are full.
How to tell:
- Smell persists after you've run water in every drain
- You hear gurgling or glug sounds when a fixture drains
- Multiple drains smell, not just one
Fix: Inspection and cleaning of the vent pipe. Usually done from the roof. Plumber service call, often under $200 if access is straightforward.
Cause #4: main sewer line problem
If running water in every drain didn't fix it, and the smell isn't obviously at one toilet, and you have gurgling/slow draining at multiple fixtures — the problem may be in the main sewer line. A partial clog, crack, or root intrusion can allow sewer gas to escape back up the system.
How to tell:
- Multiple drains are slow in addition to the smell
- Gurgling when water runs elsewhere
- Sewage smell in basements or crawlspaces (gas escaping through an underground breach)
- Unusually wet or green patches in the yard along the sewer line path
Fix: Main line camera scoping. Based on what we find, options range from cleaning to spot repair to lining to full replacement. Scoping runs $350–$500 and gives you definitive answers.
Cause #5: garbage disposal buildup
If the smell is strongest near the kitchen sink, especially when the disposal runs, the issue is food residue and bacterial growth in the disposal itself.
How to tell: Smell is kitchen-specific and worse when the disposal runs.
Fix: Clean the disposal. Ice cubes and rock salt (run the disposal with them), followed by citrus peels (lemon or orange), handles most of it. Baking soda and vinegar is also effective. If the smell persists, the disposal may need replacement — most last 10–12 years.
Put it all together
Work through the causes in order:
- Run water in every drain. Wait 24 hours.
- If the smell persists, isolate to a specific location.
- Near a toilet? Likely wax ring — call a plumber.
- Near the kitchen? Likely disposal — clean it.
- Everywhere with gurgling? Likely vent or main line — call for diagnosis.
If you've worked through #1-3 and still have a persistent sewage smell, call us at (503) 917-3259. We can diagnose the rarer causes quickly — vent pipe issues, main-line problems, or unusual cases that don't fit the common patterns.
