Sewer Camera Inspection
Run a camera through the sewer to see its condition before a home purchase or a repair decision.
Homeowner guide
Sewer Smell in the House in Louisville, CO: Causes and Fixes
Sewer gas has a rotten-egg or swampy smell, and it should not be in the house. The source is almost always one of a handful of places, and finding which one saves guessing and unnecessary repairs.
By the Flatirons Express Plumbing team ·
Where the smell is strongest
Walk the house and note where the odor is strongest. A smell concentrated in one bathroom points to that room's drain or toilet. A smell in the basement points to a floor drain or the main line. A smell in the whole house points to the vent system or the sewer.
Time matters too. A smell that appears after using water suggests a trap problem. One that comes and goes with weather can point to a vent.
Dry traps
Every drain has a trap that holds water to block gas. When a drain goes unused, the water evaporates and the barrier is gone. Basement floor drains and guest bathroom sinks are typical.
Pour water into each unused drain, then a little cooking oil to slow evaporation. In a dry climate this happens quickly, so make it a monthly habit. A trap primer on a floor drain is a permanent fix.
Toilet seals and fixtures
A toilet sits on a wax ring that seals it to the drain flange. When the ring fails, gas and sometimes water leak out. A toilet that rocks or a smell near its base are signs. Replacement is a short job.
See toilet repair for what is involved. Also check the sink overflow, the tub drain and the washing machine standpipe, which can dry out.
Where the smell points
The location and timing of the smell narrow down the cause.
| Where you smell it | Likely cause | What to try |
|---|---|---|
| One bathroom, rarely used | A dry trap | Run water in the drain for a minute |
| Around the base of a toilet | A failed wax ring or seal | Have the toilet reset |
| Near the basement floor drain | A dry trap or a blocked line | Pour water in and check for backups |
| Throughout the house | A vent or main line problem | Call for a camera inspection |
Vents and the roof
Plumbing vents let air in so drains flow and keep gas moving up and out. A vent clogged by a bird nest, leaves or frost can push gas back into the house. A cracked vent in the attic leaks gas there.
A plumber can check the vent from the roof or with a camera. Winter frost closing a vent opening is a real problem in cold climates, and it clears when it warms.
Cracked or damaged sewer lines
A crack in the drain line or the lateral leaks gas, and sometimes waste, into the ground or the crawl space. A smell outdoors or in the basement, with slow drains, suggests this.
A sewer camera inspection shows the pipe. If a break is found, sewer line repair covers the options. Expansive clay soil can shift a lateral and open a joint.
Rule out the simple things first
Run water in every drain for a minute, including the basement floor drain, and pour water into any trap you do not use. Check the toilet seal for rocking or water at the base. Clean out the garbage disposal, which can hold decaying food.
Smell near a washing machine standpipe can mean a dry trap or a missing cap. Smell near a sump pit can mean the lid is not sealed. Narrowing the location points you to the cause quickly.
When to bring in help
A smell that does not change after the simple fixes, or that comes with slow drains and gurgling, deserves a professional look. A camera shows cracked pipe, a belly that holds waste and root damage. See sewer camera inspection for how that works.
Do not ignore a persistent odor. Sewer gas contains compounds that can make people unwell, and the source is often a defect that grows worse over time.
Ventilation and the roof
Plumbing vents carry sewer gas up through the roof. A vent blocked by a bird nest, ice or debris can send odor back into the house. A mild odor that comes and goes with the wind or the weather can point to a vent issue.
Do not climb onto a snowy or icy roof to check a vent. A professional can inspect it safely. If the smell comes only when a particular fixture drains, the trap or the fixture's own vent is a better suspect.
Smells that need a faster response
A rotten-egg odor may come from sewer gas, but natural gas also carries an added odor so you can detect a leak. If you are unsure which it is, treat it as gas: leave the house and call 911 or the gas utility from outside.
Strong sewage smell with water on the floor, or a backup in a tub or floor drain, is urgent. Stop using water and call. Waste in the home is a health concern, and cleanup is best done with gloves and proper disinfectant or by a professional.
Safety
Sewer gas contains hydrogen sulfide and methane. At low levels it is unpleasant. At high levels it is hazardous, and methane can be explosive. Ventilate the area, avoid ignition sources and call a plumber if you cannot find the source.
If anyone feels dizzy or ill, leave the house and get fresh air. A persistent smell should not be ignored.
Quick answers
Sewer smell questions
It can be. Hydrogen sulfide at higher levels is harmful, and methane is flammable. Ventilate and find the source.
A dry floor drain trap is the most common cause. Pour water in it. If the smell stays, the line may be damaged.
Yes, if the wax ring has failed. A toilet that rocks is a clue.
A trap that dries out between uses, or a vent that clogs in some weather, can cause it.
Services that connect to this topic
Sewer Line Repair
Mend a sewer pipe that is cracked, shifted or full of roots, whether the fix is one spot or a long run.
Toilet Repair & Installation
Cure a toilet that runs, rocks, leaks or clogs, or install a replacement.
Keep reading
Tree roots in your sewer line
Roots find tiny gaps in sewer pipes and grow into blockages. Learn the signs, the fixes and how to prevent a repeat.
Tiny flies at the drain and how to end them
Small flies that keep landing near a sink, tub or basement floor drain are breeding in the pipe. Confirm it, clean it and watch for bigger trouble.
A toilet that refuses to flush
Most flush failures are a tank problem or a clog. Check the water level, the flapper and the chain before you call.
Odor that will not clear?
Say where the smell is strongest when you call. A dispatcher can connect you with a local contractor.