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Sewer gas smells occur when the plumbing system fails to keep wastewater gases sealed inside pipes. Every drain relies on water-filled traps and proper venting to block those gases. When either system fails, sewer odors escape into living spaces.
Most sewage smells in the house come from one of the five causes below:
A dry P-trap is the leading reason homeowners notice a sewage smell in the house. The curved section of pipe beneath sinks, tubs, showers, and floor drains is designed to hold water and block sewer gas. When that water evaporates, odors move freely indoors.
This is especially common in:
This explains why a bathroom smells like sewage after you’ve been away, or why an unused drain suddenly starts to smell without any visible leak.
Drain pipes can leak sewer gas even when no water is escaping. Aging slip joints, worn gaskets, corroded piping, or improperly sealed connections allow odors to seep out, especially when water flows through the system.
Warning signs include:
Older homes are particularly vulnerable, especially where plumbing has been modified over time.
Plumbing vents regulate air pressure and allow sewer gases to exit safely through the roof. When vents are blocked or damaged, pressure builds and forces gas back through traps or weak pipe joints.
Common vent problems include:
Symptoms often include gurgling drains, slow drainage, and odors that come and go depending on weather or water usage.
When the main sewer line becomes restricted, sewer gas and wastewater are pushed back toward the home. Causes include tree roots, grease buildup, foreign objects, and pipe collapse.
Red flags include:
This is not a DIY situation and requires immediate professional evaluation.
Biofilm is a slimy layer of bacteria that builds up inside drains, especially in kitchen sinks, shower drains, and garbage disposals. It can produce a rotten egg or sewage-like odor even when surfaces look clean.
This is why:
Using baking soda and vinegar for a smelly bathroom sink can help with surface-level buildup, but persistent odors often indicate deeper accumulation inside branch lines. In these cases, professional drain cleaning is often the fastest and most effective way to eliminate the smell at its source.
Bathrooms: Dry traps, failed toilet wax rings, and biofilm are the most common causes. A sewage smell near the toilet base may indicate a failing seal, even without visible leaks.
Kitchens: Grease buildup feeds odor-causing bacteria. Dishwashers and disposals sharing a drain line can spread smells between fixtures. Drain deodorizers may help briefly but do not remove buildup.
Laundry rooms and basements: Floor drains dry out quickly in winter. Missing cleanout caps, unsealed sump pits, and failed trap primers are frequent odor sources in Eastern Washington and Northern Idaho homes.
Before calling a plumber, there are a few simple, low-risk checks you can safely do at home. These steps help rule out common causes like dry traps or surface buildup, but they won’t resolve deeper venting or sewer line problems.
If odors persist after these steps, the source is likely structural or in the sewer line.
Yes. Sewer odors can be harmful, especially when they are strong, persistent, or widespread. Sewer gas commonly contains methane and hydrogen sulfide. At low levels, exposure may cause headaches, nausea, dizziness, fatigue, and eye or throat irritation. At higher concentrations, hydrogen sulfide is toxic, and methane can become explosive in confined or poorly ventilated spaces.
Sewer odors should be treated as urgent if you notice:
If these signs are present, ventilate the area if you can do so safely, leave the space, and contact a licensed plumber immediately. Bulldog Rooter offers 24/7 emergency service to help identify the source and restore safe conditions quickly.
Sewer odors are rarely guesswork problems. They require accurate testing to find the exact failure point and fix it correctly the first time. Bulldog Rooter uses professional diagnostic tools, including smoke testing, camera inspections, and targeted pressure checks, to identify where sewer gas is escaping and why.
Once we pinpoint the cause, we explain what’s happening in plain language and walk you through your options. Whether the issue is a dry or failed trap, a toilet seal, venting problem, drain buildup, or a main sewer line concern, our team handles the repair with clear pricing and no surprises.
Homes in Spokane, Spokane Valley, Liberty Lake, Post Falls, and Coeur d’Alene face unique challenges, from winter vent blockages to older plumbing layouts, and we test with those local conditions in mind.
If a sewage smell in your house lasts more than a day, keeps coming back, affects multiple rooms, or causes symptoms, it’s time to call. Bulldog Rooter is available 24/7 with fast response times, experienced plumbers, and straightforward estimates you can trust.