Drain Smells Like Sewage After Rain

Drain issue related to: drain smells like sewage after rain

Quick Answer:

If you notice a sewer smell from a floor drain or sink right after heavy rain, it often means the storm stressed the local sewer or a trap lost its water seal. Start by confirming the smell happened while or just after the rain, check the lowest drains in the house, and run water to refill traps. If several fixtures smell or slow, or the outdoor cleanout is high or overflowing, call a plumber.

Why This Happens

  • Stormwater can overload municipal sewers or private laterals, pushing air and sewage odors back into low points like basement floor drains.
  • Dry or siphoned traps (the curved pipe under a drain) let sewer gas into the room. Heavy flow or strong venting can siphon water from traps during a storm.
  • Downspouts, yard runoff, or a damaged sewer lateral can let extra water into the system and change pressure in the line, producing smells after rain.

Step-by-Step What to Do

1) Confirm the timing

  • Make sure the smell began while it was raining or within a short time afterward. That link to weather makes a rain-caused sewer issue more likely.
  • Note whether the smell clears as the storm eases.

2) Check the lowest drains first

  • Start with basement floor drains, laundry or utility sinks, and any basement toilets — these will show problems first if the main line is stressed.
  • Look for standing water, slow drainage, or water backing into a nearby fixture.

3) Run water to refill traps

  • Pour a bucket (or run each fixture) so the U-shaped trap fills — a visible water seal stops sewer gas. Do this for floor drains, sinks, tubs, and toilets.
  • If a drain immediately loses its water level, that suggests siphoning or a leak in the trap.

4) Look for trap siphoning or venting problems

  • Listen for gurgling when other appliances run; that can indicate air moving through traps. If you hear gurgling, see Drain Gurgles When You Run the Sink for more context.
  • If you see bubbles in a toilet or sink while another fixture runs, that points to pressure changes in the drain system — see Drain Bubbles When the Toilet Flushes.

5) Note whether multiple fixtures smell or are slow

  • One isolated drain that smells after rain is often a trap issue. Multiple slow or smelly fixtures suggest a main-line or municipal issue.
  • Record which fixtures are affected and whether the problem is worse during and immediately after storms.

6) Inspect the outdoor cleanout level if accessible

  • Check the sewer cleanout at or just outside the foundation for high water, odors, or overflow. If the cleanout is bubbling, full, or dirty, that’s a sign of a surcharge in the line.
  • Do not open the cleanout without proper protection (see What Not to Do).

What Not to Do

  • Do not pour drain-cleaning chemicals into a line that may be partially backed up — chemicals can splash back, create dangerous fumes, and make the real problem harder to diagnose.
  • Do not open an outdoor cleanout or sewer cap without protection like gloves, goggles, and a mask; sewage can spray out under pressure.
  • Do not ignore repeated smells tied to rain. Occasional odors that resolve quickly are different from recurring, storm-linked events that can signal a failing lateral or municipal issue.

When to Call a Professional

  • There is actual sewage backing into the house or a cleanout is overflowing.
  • Multiple fixtures are slow or emitting sewage odors, especially after each rain.
  • You find standing sewage near the foundation or see water coming up through a floor drain.
  • Simple fixes (refilling traps) don’t stop the smell or the cleanout shows signs of pressure or water buildup.
  • If you suspect a damaged sewer lateral, tree-root intrusion, or municipal sewer surcharge — a plumber or utility should inspect and test the line.

Safety Notes

  • Avoid direct contact with sewage. Wear gloves and eye protection if you must inspect drains.
  • Ventilate the area if the odor is strong, but don’t create electrical hazards with fans in standing-water situations.
  • Do not mix cleaning chemicals; that can produce toxic gases.
  • If a cleanout must be opened, use proper PPE and be prepared for sewage under pressure; when in doubt, call a pro.
  • Document the problem (photos, times, weather) to help a plumber or your local utility diagnose recurring issues.

Common Homeowner Questions

  • Will pouring water down the drain stop the smell? Yes, refilling traps often stops odors temporarily if the trap was dry or siphoned.
  • Can a plunger fix this after rain? A plunger might help a single clogged fixture, but it won’t fix a pressurized or overloaded sewer line.
  • Is this a homeowner fix or does it need a plumber? Refill traps and check the cleanout visually first; call a plumber if sewage is present, multiple fixtures are affected, or the issue repeats after each storm.

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