Pasadena Pipe Works hears this question often. Take a pitcher of tap water to the drain that smells, empty it down, and give it a day. If the odor was coming from a dry trap, it is gone. If it is back, the cause sits somewhere else: a worn seal under a toilet, a blocked roof vent, or a crack in the pipe that runs out to the street. Before you do anything else, make sure it is not natural gas, because the two can smell alike, and the first section below tells you what to do. This page takes the causes in order, cheapest first. If you reach the end and still smell it, the quote form puts a plumber on the way to your Pasadena or San Gabriel Valley address.
Could this actually be a gas leak?
Raw natural gas has no smell, so SoCalGas adds a rotten-egg odorant, and that is close to what sewer gas smells like. If you cannot tell them apart, act as though it is gas. Walk out, then call SoCalGas from the sidewalk on 1-800-427-2200. Dial 911 as well when anyone's safety is at stake. Touch no light switches and strike no flame on the way.
SoCalGas also warns that your nose can fail you, since odor fade or a stuffy nose can hide a leak. That is another reason not to guess at the source. A real sewer smell tends to be damp, musty and tied to a drain or fixture, while a gas smell can show up near the stove, the water heater or the furnace. If a gas appliance is anywhere near the odor, call first and sort out the drain later.
Where is the rotten-egg odor coming from?
Nearly always one of five culprits: a trap that dried out, a toilet seal that gave up, a vent pipe that is blocked or split, a damaged drain line, or a cleanout missing its cap. Plumbing guides rank the dry trap first. Each sink, tub and floor drain holds a plug of water that blocks gas, and that plug can evaporate.
Read down the left column and find your symptom:
| What you notice | Likely cause |
|---|---|
| One bathroom or one drain, worse after weeks of no use | Dry trap |
| Strongest at the base of one toilet, maybe a damp edge | Worn wax ring |
| Every drain smells, gurgles when water runs | Blocked vent or a main line problem |
| Smell in the yard or garage as well as the house | Damaged line or open cleanout |
| Smell only after a washer or tub empties | Trap siphoned by a vent problem |
Sewer gas is a mixture. Hydrogen sulfide gives it the rotten-egg note and methane is odorless but flammable in enclosed spaces, which is why odor should never be ignored for long.
Which fix works fastest?
Start with the free fix. Run water for 30 seconds into every drain, and do not forget the floor drain by the water heater and the guest shower nobody uses. A dry trap refills in seconds and the smell fades within the hour. In a floor drain that dries again, a spoon of mineral oil floating on the water slows the evaporation.
Next, clean the drain itself. Slime in an overflow hole or around a stopper can smell like sewage with no sewer problem at all. A bottle brush and hot water reach most of it. Skip bleach mixed with other cleaners: the fumes are worse than the smell. If a toilet's base smells, tighten nothing yet and read our toilet repair guide for how the seal below it is checked.
Air fresheners and enzyme drops only mask a problem. A cracked pipe or broken seal cannot be dosed away, and a smell that returns after the water fix needs a person to look.
Can sewer smell in a house make you sick?
At household levels, usually it causes headaches, nausea and eye or throat irritation, not serious illness. Hydrogen sulfide is the culprit: low exposure irritates, while very high concentrations in enclosed spaces are dangerous, though those levels are not found in a living room. Persistent smell with symptoms is a reason to ventilate and fix the source.
Do not wait if anyone in the home gets dizzy or very short of breath, or if the smell is overpowering. Open doors, step outside and call for help. For ordinary background odor, the aim is to find the cause within a few days and not live with it for months. Children, older relatives and anyone with asthma are the ones to protect first.
Why does the smell come and go, and why in the cold?
An intermittent smell points to something that changes with conditions. Traps dry out in warm, dry spells and rarely used fixtures lose their seal; vents can pull odors in on windy days; and a heater or fan running in winter shifts air pressure inside the house, drawing odor from a weak seal. Smells that appear only when it is cold often trace to that air movement, not freezing.
Pasadena rarely freezes, so frozen vent caps are not a typical cause here. What is more likely is a dry winter spell, long gaps between uses in a spare bathroom, or a door and window setup that changes how the house breathes. Jot down the hour, the weather and whichever fixture ran last. Three lines like that tell a plumber more than a long description.
When does a sewer smell mean the line itself is damaged?
If all the drains smell, if the pipes gurgle, when the odor is also in the yard, or when a drain backs up. Pasadena houses with aging iron or clay laterals, tree roots and shifted joints are prone to it, and the trouble grows instead of fading. A plumber feeds a camera through the pipe to find the spot that is split, offset or choked.
Repair options depend on what the camera shows. Digging up the yard to replace a section is the traditional method. Trenchless sewer repair, by lining or bursting the old pipe from small access holes, leaves the lawn, driveway and landscaping mostly intact and suits some, though not all, failures. The plumber decides between them from the footage and the layout. Main line work often calls for a permit, and the state's contractor license rule applies at $1,000 and above.
Cleaning a blocked main is a separate job from repairing a broken one. If the smell comes with slow drains, our page on the clogged vent pipe covers one cause, and the cast iron pipes page explains why old iron fails the way it does.
How do I unclog a main sewer line myself?
A homeowner can try a cleanout access and a rented drain auger, but a main line is the point where DIY usually stops paying off. The cleanout is the capped stub near the house or the lot line. Keep upwind of it and ease the cap off. If sewage is rising, stop and call: wastewater carries bacteria, and a mistake floods the yard.
Skip the drain chemicals when a line is already backing up: they pool in standing water and burn skin and pipe. If a plumber's auger or camera is needed, expect a written price before the work starts. After a blockage is cleared, ask for a camera look at the same visit so you know whether roots or a break caused it, and restore the cap tightly so the smell does not return.
Common questions
Can one dry trap really make the whole room stink?
Yes, and it is the most frequent cause. The curved pipe under each fixture keeps a small pool of water that blocks gas. A bathroom left idle for several weeks can lose that pool to evaporation. Running water for half a minute restores it, and the smell should go within the hour if the trap was the reason.
Is a smell outside the house a separate problem?
Often, yes. A yard smell near the house can mean an open or loose cleanout cap, a cracked line outside the foundation or a vent terminating at ground level. Indoors, traps and seals are more likely. If both are present at once, the odds shift toward a damaged underground section and a camera inspection.
Will pouring bleach or vinegar down the drain stop the smell?
Not for long. Cleaners can freshen a slimy drain but they do not seal a cracked pipe or restore a worn wax ring. Never mix bleach with vinegar or other cleaners, because the fumes are harmful. Use plain water to refill traps, and if the smell stays, treat that as a sign of a structural cause.
Will my homeowner policy cover a broken sewer line?
That turns on the wording. Plenty of policies cover sudden damage but exclude wear, roots and old pipe, while some sell an add-on for sewer lines. Check with your agent first, and save the camera video and photos for the adjuster.
How do I tell a sewer smell from a gas leak?
Both can read as rotten eggs, so doubt means treat it as gas. Gas shows up near the stove, furnace or water heater; sewer smell hangs around drains. Unsure? Go outside, phone SoCalGas on 1-800-427-2200 and let the crew confirm. A lit match is never the test.
Our other plumbing services are listed on the Pasadena Pipe Works home page.
Sources
- Sewer gas, Wikipedia
- SoCalGas, natural gas leaks
- California Contractors State License Board, what kind of contractor do you need
- Published guides on sewer odor causes from several plumbing and restoration companies, checked November 2026
Page updated