How to Get Rid of Drain Smell (Sewer / Rotten Egg)
Persistent sewer gas smell that does not resolve with trap refilling could indicate a plumbing vent problem or cracked sewer pipe. Sewer gas contains methane and hydrogen sulfide, both of which are hazardous in enclosed spaces. If the smell is strong and persistent, call a plumber.
What You'll Need
- 1/2 cup
- 1 cup
- Full kettle
- 2 tbsp
Step-by-Step Method
Determine which drain the smell is coming from. Run water in each drain for 30 seconds. If the smell comes from a drain you rarely use, the P-trap has likely dried out.
P-traps (the U-shaped pipe under every drain) hold water that blocks sewer gas. If a drain is rarely used, the water evaporates. Pour 2 cups of water down the drain to refill the trap. Add 2 tbsp mineral oil on top to slow future evaporation.
For drains you use regularly: pour 1/2 cup baking soda down the drain, follow with 1 cup white vinegar. Let fizz 15 minutes. Flush with boiling water. This removes biofilm buildup that produces odor.
If the smell persists after refilling traps and cleaning, the issue may be a cracked drain pipe, failed wax ring (toilets), or blocked vent stack. These require a plumber.
- Do not pour bleach down drains regularly (corrodes pipes and kills beneficial bacteria in septic systems)
- Do not ignore persistent sewer smell (could indicate a gas leak or broken sewer line)
- Run water in every drain in your home at least once a month to keep P-traps full.
- Basement floor drains are the most commonly dried-out traps because they are rarely used.
- The mineral oil trick: a thin layer of oil floats on top of the water in the P-trap and dramatically slows evaporation.
Frequently Asked Questions
Two possible causes: a dried-out P-trap allowing sewer gas to enter (easy fix: pour water down the drain), or hydrogen sulfide produced by bacteria in the biofilm coating the inside of the drain pipe (fix: baking soda + vinegar cleaning). If neither fixes it, you may have a plumbing vent obstruction or cracked pipe.
Sources & Methodology
P-trap water seal is the standard sewer gas barrier in residential plumbing. Mineral oil evaporation barrier is a recognized maintenance technique for seldom-used drains.
Last reviewed: March 20, 2026