Sewer Smell in the House: How to Find and Fix It
Updated September 18, 2026
Can I do this myself?
DIY with precautions
Most sewer smells come from dry traps or dirty drains and are safe to fix yourself. If the smell is strong, persistent or you feel headaches or dizziness, ventilate, leave and call a plumber. Roof vent work is for a pro.
A sewer smell inside the house almost always means sewer gas is getting past one of the barriers designed to keep it out. Every drain has a trap (a U-shaped bend, called a P-trap under sinks, or built into toilets and floor drains) that holds a small plug of water to block the gas. Toilets are sealed to the drain pipe by a wax ring or rubber seal. And vent pipes through the roof let gas escape outside and keep the traps from being siphoned dry.
When the water in a trap evaporates, a toilet seal fails, or a vent is blocked, you smell it. The fix is often as simple as running water into a drain you rarely use. Other times it is gunk built up in a sink overflow or drain, or a toilet that needs a new seal.
Sewer gas contains hydrogen sulfide, which smells like rotten eggs, and methane. In the small amounts from a dry trap, it is unpleasant rather than dangerous, but high concentrations can be harmful. And natural gas and LPG are given a similar rotten egg smell on purpose. If you aren’t sure which you are smelling, or the smell is strong and near gas appliances, treat it as a gas leak: leave and call your gas utility from outside.
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Signs of the problem
- A sewage or rotten egg smell near a sink, shower, floor drain or toilet
- Smell that is worse in a room or drain you rarely use
- A smell around the base of a toilet, possibly with water on the floor
- Gurgling drains or slow draining alongside the smell
- Smell coming from the sink overflow hole
- Smell that is stronger on windy days or when other fixtures drain
Common causes
Dry trap
Most commonTraps in guest bathrooms, basement floor drains, unused showers and utility sinks lose their water seal through evaporation. Running water for a few seconds refills them. This is the most common cause.
Dirty drain or overflow
Most commonHair, soap, toothpaste and food build up in drains and in the overflow channel of bathroom sinks and tubs, where bacteria produce a sewage-like odour.
Failed toilet wax ring or seal
SometimesIf a toilet rocks, or there is a smell or water at its base, the seal between the toilet and the drain pipe may have failed, letting gas and sometimes water escape.
Blocked or missing vent
SometimesLeaves, nests or ice can block the roof vent. Without venting, draining water can siphon traps dry, and you may hear gurgling. Working on the roof vent is a job for a professional.
Cracked pipe or loose connection
Less commonA cracked drain pipe, a loose cleanout cap, or a poorly sealed connection behind a wall or under a floor can let gas out. These often need a plumber to find, sometimes with a smoke test.
Safety first: before you start
- Critical:If you can’t tell whether it is sewer gas or a gas leak (both can smell like rotten eggs), treat it as a gas leak: leave the building and call your gas utility or emergency number from outside.
- Critical:If the smell is strong or persistent, or anyone has a headache, dizziness, nausea or eye irritation, open windows, leave the area and call a plumber.
- Ventilate while you work: open windows and run the bathroom fan.
- Never mix drain cleaners, bleach and other cleaning chemicals. Some combinations release toxic gases.
- Wear gloves when cleaning drains and overflows, and wash your hands afterwards.
- Don’t go on the roof to check vents. Leave that to a professional.
Tools & materials
Tools
- Flashlight
- Small bottle brush or flexible drain brush
- Screwdriver (to lift drain covers)
- Plastic drain-cleaning strip or hair snake
- Rubber gloves
Materials
- Water (a jug or bucket)
- Baking soda and white vinegar, or an enzyme drain cleaner
- A little cooking or mineral oil (for rarely used floor drains)
- Replacement toilet wax ring or rubber seal (if needed)
Step-by-step fix
- 1
Rule out a gas leak
Ask yourself where the smell is strongest. Near a drain, toilet or sink, it is likely sewer gas. Near a stove, gas water heater, furnace, LPG cylinder or gas meter, or everywhere at once, treat it as a gas leak and leave immediately.
Warning: When in doubt, get out and call your gas utility or emergency number from outside. See the gas smell guide.
- 2
Ventilate the area
Open windows and turn on exhaust fans. If the smell is overwhelming, or anyone feels unwell, leave the room and call a plumber rather than investigating.
- 3
Refill every trap
Run water into every sink, shower, tub and floor drain for 30 seconds, including rarely used ones in guest bathrooms, basements and laundry rooms. Flush toilets that haven’t been used for a while. If the smell fades within an hour or so, a dry trap was the cause.
Tip: For floor drains that are rarely used, pour a spoonful of cooking or mineral oil on top of the water after refilling. It slows evaporation.
- 4
Clean the sink overflow
Bathroom sinks and tubs have an overflow opening near the rim. Scrub inside it with a small bottle brush, then pour a little baking soda in followed by vinegar, wait 15 minutes and rinse with hot water from the tap.
- 5
Clean the drain itself
Remove the stopper or drain cover and pull out hair and gunk with a plastic drain-cleaning strip. Scrub the drain opening with a brush. Flush with hot tap water. An enzyme drain cleaner used as directed can help break down residue further down.
Warning: Don’t mix chemical drain cleaners with bleach, vinegar or other products. Toxic fumes can result.
- 6
Check the toilet seal
Try gently rocking the toilet. If it moves, or the smell is strongest at its base, or you see water or staining around it, the wax ring or seal has probably failed. Replacing it involves shutting off the water, removing the toilet and fitting a new ring. See the toilet leaking at base guide, or call a plumber.
- 7
Listen for gurgling
If drains gurgle when a toilet flushes or a tub drains, and traps seem to go dry quickly, the vent may be blocked. Don’t climb onto the roof. A plumber can clear or inspect the vent safely.
- 8
Check cleanouts and exposed pipes
In basements and utility areas, look for loose or missing cleanout caps on drain pipes, cracked pipes or damp spots. A missing cap should be replaced; cracked pipes need a plumber.
- 9
Call a plumber if the smell remains
If the smell persists after refilling traps and cleaning, a plumber can find hidden leaks, sometimes with a smoke test that shows where gas escapes from the drain system.
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How to check it's fixed
- The smell is gone within a day of refilling traps and cleaning
- Drains run freely without gurgling
- The toilet doesn’t rock and there is no smell or water at its base
- The smell doesn’t return after a few days
When to stop and call a professional
- The smell is strong, persistent, or anyone feels ill (ventilate and leave first)
- You aren’t sure whether it is sewer gas or a gas leak (call your gas utility first)
- Drains gurgle and traps keep drying out (possible blocked vent; roof work is for a pro)
- The toilet rocks or leaks at the base and you aren’t confident removing it
- There is sewage backing up into drains or a cracked drain pipe
- The smell continues with no obvious source
How to prevent it
- Run water in rarely used drains every week or two.
- Clean sink overflows and drains every few months.
- Use drain strainers to catch hair and debris.
- Keep grease, wipes and food waste out of drains and toilets.
- Have a plumber inspect vents if you notice regular gurgling.
Frequently asked questions
Is sewer gas dangerous?
In the small amounts from a dry trap, sewer gas is unpleasant but usually not harmful. In high concentrations, the hydrogen sulfide and methane it contains can be hazardous. If the smell is strong or anyone feels unwell, ventilate, leave and call a plumber.
How do I tell sewer gas from a gas leak?
Both can smell of rotten eggs. Sewer gas is usually strongest at a drain, toilet or floor drain. A gas leak is usually near gas appliances, the meter or an LPG cylinder, or all through the house. If you can’t tell, treat it as a gas leak and leave.
Why does my bathroom smell like sewage only sometimes?
Intermittent smells often come from a trap that slowly dries out, a vent that is partly blocked (worse on windy days or when other drains run), or a toilet seal that leaks only when the toilet is used.
Can a dry P-trap cause a sewer smell?
Yes, it is the most common cause. The trap’s water seal blocks sewer gas. If a drain isn’t used for weeks, the water evaporates and gas comes through. Running water for 30 seconds fixes it.
Will bleach get rid of a drain smell?
Bleach can mask odours briefly but won’t fix a dry trap, a failed seal or a blocked vent. Never mix it with other drain products. Cleaning the drain mechanically and refilling traps works better.
This guide is general information, not professional advice. Homes differ, so follow your product manuals and local codes. If anything looks different from what's described, or you feel unsure, stop and call a qualified professional. In an emergency, leave the area and call your local emergency number.
Related guides
Gas smell
EmergencyThis is an emergency, not a DIY repair. Leave the building now and call for help from outside; do not try to find or fix the leak yourself.
Slow-draining sink
Safe to DIYYes, clearing a slow sink drain is a safe DIY job with basic tools. Skip chemical drain cleaners, and call a plumber if several drains back up at once or dirty water comes up in other fixtures.
Toilet leaking at base
DIY with precautionsReplacing a wax ring is a manageable DIY job, but the toilet is heavy and awkward to lift, and the leaking water is often contaminated. Get a helper for lifting, and call a pro if the floor is soft or the flange is broken.
Leak under sink (P-trap)
Safe to DIYYes, a leaking P-trap is one of the easiest plumbing repairs. It is a low-pressure drain part, so there is no need to shut off the water, just stop using the sink. Call a pro if the leak comes from the wall pipe or the cabinet floor is rotting.
Clogged toilet
Safe to DIYYes, most toilet clogs are safe to clear yourself with a flange plunger or a toilet auger. Stop and call a plumber if sewage is coming up in other drains, or if water is spreading toward outlets or through the floor.