First rule: if the smell is rotten eggs, it could be natural gas rather than sewage, because utilities add that odor on purpose. Treat it as gas until proven otherwise, get outside, then telephone SoCalGas (1-800-427-2200). If the air is clearly sewage, work through the checks below. Most causes are cheap. Wider help sits on the Sunset Coast Plumbing home page if you are unsure which service you need.
Is it sewer gas or a natural gas leak?
Sewage smells like rotten food and drains. Utility gas has a sharp rotten-egg note and tends to be strongest near the stove, water heater or furnace. Cannot tell? Skip lighters and light switches, leave, and let the utility decide from outside. 911 is there if anyone is at risk. A false alarm costs nothing.
Sewer gas itself is a mix of methane and hydrogen sulfide among others. In small amounts it is mostly a nuisance. Strong, constant odor with headaches, dizziness or nausea means open windows, leave the room and get help. Methane can also burn, so no flames or smoking near it.
Which part of the house is the smell coming from?
Narrow it by sniffing at one spot at a time. A smell strongest at one bathroom sink or floor drain points to a dry trap. One toilet points to its seal. Odor in the garage or near the washer suggests a floor drain or washer standpipe. Odor everywhere, or only outdoors beside a cleanout, implicates the main line or a vent.
Keep notes on timing: after a shower, during rain, only in the morning, after the dishwasher drains. Patterns help the plumber. A smell that arrives after heavy rain on a hillside lot can mean runoff pressing on a cracked line, and one that comes only after laundry points to the washer drain.
What are the cheap fixes to try first?
Run water in every seldom-used drain for a minute, including the guest shower, laundry sink and garage floor drain, then pour in a cup of water to top up the trap, the U-bend whose standing water seals out gas. It evaporates in weeks, particularly in the dry Westside summer. Add a spoon of mineral oil to slow evaporation.
Then check the toilet base for rocking or moisture, which suggests a failed wax ring. Clean the garbage disposal and the overflow hole on sinks, since food film also smells. Our walkthrough on getting rid of sewer smell and the guide to causes of sewer gas smell go through each fix.
Could the sewer line itself be cracked?
Think sewer line when the smell is persistent, shows up in several rooms, comes with slow drains or gurgling toilets, or arrives with wet patches in the yard. Older houses, built roughly 1900 to 1950, commonly have clay or cast iron laterals under the lawn, which crack, corrode or fill with roots, and the odor leaks into the soil and crawlspace before it reaches your nose.
A plumber confirms the diagnosis with a sewer camera pushed down the cleanout, which shows cracks, sags, roots and offsets on screen. Ask to see the footage. If the line is damaged, the fix may mean digging in the yard under an excavation permit, through a spot repair or a pipe liner. The camera inspection price belongs on the written quote.
What about vents, wax rings and other hidden causes?
A blocked roof vent starves drains of air, so traps siphon dry and gas escapes. Birds, leaves and debris are common in canyon neighborhoods with big trees. A failed wax ring at a toilet flange leaks tiny amounts of gas at the base. Cracked or glued-loose drain fittings inside walls are another source, and a smoke test finds them.
A smoke test pumps harmless visible smoke into the drain system and shows where it escapes, a quick way to locate a leak without opening walls. The price is covered in smoke test cost. Always ventilate the home before and after, and tell neighbors if the smoke might appear in shared walls or yards.
Can I stay indoors while the smell is there?
For a faint, occasional odor, yes, with windows open while you track it down. For a strong or constant smell, anyone with a headache, dizziness, or breathing trouble, leave and ventilate. Children, pets and people with lung conditions react first. A sudden gush of sewage into a tub or toilet, a backup, is a plumbing emergency; stop running water throughout the house.
Keep caustic drain cleaners out of a line that may be damaged; they can eat pipes and hurt anyone who later opens it. Do not mix cleaners, because bleach with ammonia products makes toxic gas. If you suspect a backup, see why a drain runs slowly.
Common questions
How much of a day does tracking it down take?
Checking traps, a wax ring or a vent can fill an hour or two. A camera inspection adds time, as does a smoke test. If digging is needed the repair is scheduled separately, since it involves permits and marking underground utilities. The first visit finds the cause and gives you the options and a written price.
What questions are worth asking the plumber?
Find out how the cause will be diagnosed, whether you keep the camera video, and who applies for any permit. Request the figure in writing. California asks for a contractor license on jobs from $1,000; you can confirm a number with the state. Also ask whether a repair without digging is possible.
Is anyone needed on site?
An adult who can point out where the smell is worst and open up the cleanout, garage and crawlspace makes the visit faster. Mention pets and locked gates when you book. If you are away, you can arrange access through someone you trust, though the plumber will want a phone number for questions.
Can a bad smell appear after a vacation?
Yes. Traps dry out in a few weeks, so a house left empty can smell when you return. Run every faucet and drain for a minute and the odor should fade. If it lingers after a day, look for a cracked line or a failed seal and book an inspection through the quote page.
Can sewer smell come from the yard outside?
Yes. A cracked lateral or a missing cleanout cap can smell outdoors. A smell by the cleanout points at the line itself. Report it to the plumber with the spot where you notice it, and avoid digging around it yourself, since utilities may run nearby.
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