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Sewer smell in the house: where it comes from

Short answer

Most sewer smells come from a trap that has lost its water seal, usually a floor drain, an unused shower or a basement sink. Pour water into every rarely used drain first. If the smell stays, the next suspects are a sink's overflow channel, a failed toilet wax ring, a blocked vent and a loose cleanout cap; a cracked drain pipe is less common but possible.

Updated · Editorial team; not yet technically reviewed

Square stainless steel shower floor drain in white tile

Sources, from most to least likely

  • Dry trap

    Most common

    Tell: Smell near a floor drain, guest shower or utility sink that's rarely used.

    Fix: Run water for 30 seconds. A spoon of mineral oil on top slows evaporation in floor drains.

  • Dirty sink overflow

    Most common

    Tell: Smell right at a bathroom sink; the drain itself is clean.

    Fix: Scrub the overflow opening with a bottle brush and flush it with hot water and a little bleach solution.

  • Toilet wax ring

    Possible

    Tell: Smell around the toilet base; the toilet may rock.

    Fix: Reset the toilet on a new seal.

    Toilet Repair →

  • Blocked vent or failed air admittance valve

    Possible

    Tell: Smell plus gurgling drains.

    Fix: Clear the vent or replace the valve.

  • Loose or missing cleanout cap

    Possible

    Tell: Smell in the basement or crawl space near the main drain.

    Fix: Replace or tighten the cap.

  • Cracked drain or sewer pipe

    Less common

    Tell: Persistent smell in one area, sometimes damp soil or insects near the foundation.

    Fix: A smoke test or camera inspection finds it.

    Sewer Line Repair →

A 15-minute search

  1. Run water everywhere

    Every sink, tub, shower and floor drain, including the basement and guest rooms.

  2. Sniff at each fixture

    The smell is strongest at the source. Check the overflow hole on sinks separately from the drain.

  3. Check the toilets

    Rock each one gently. Movement or a smell at the base points to the seal.

  4. Look at the cleanout

    Usually a capped pipe in the basement, crawl space or outside near the foundation.

Sewer gas or natural gas?

Sewer gas smells of rotten eggs mixed with general sewage. Natural gas utilities add a sulfur-like odorant, so the two can be confused. If the smell is strong, sudden, or near a gas appliance, leave the house and call the gas utility from outside. See what to do if you smell gas.

Sewer gas in a house is unpleasant, and at high concentrations in an enclosed space it's a health concern. A persistent smell is worth tracking down rather than masking.

When to call a plumber

  • Refilling traps and cleaning overflows doesn't help.
  • The smell comes with slow drains or gurgling.
  • You smell it outside near the sewer line or see soggy ground over it.

More questions

Why does my bathroom smell like sewage only sometimes?

Intermittent smells often come with wind or heavy water use: a partly blocked vent lets traps siphon when large volumes drain, so the smell comes and goes.

Can a washing machine cause a sewer smell?

Yes. A standpipe without a proper trap, or a hose pushed too far into the standpipe, can let sewer gas out.

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