Sewer Smell Source Finder: Where Is That Smell Coming From?

Headaches, dizziness, or nausea along with a strong smell mean you should stop troubleshooting and get out of the space.

1. Get everyone, including pets, outside.
2. If you think gas has built up in an enclosed space, call the fire department from outside.
3. Don't use matches, lighters, or anything that could make a spark on your way out.
4. See a doctor if symptoms continue after you're in fresh air.
5. Have a plumber find the source before you go back to using that space.

Utilities add a rotten-egg odor to natural gas. Near a gas appliance or gas line, treat that smell as a gas leak until someone proves otherwise.

1. Leave the building on foot, and take everyone with you.
2. Don't flip light switches, use a phone inside, or start anything that could make a spark.
3. From a safe distance, call 911 or your gas company's emergency line.
4. Don't go looking for the leak yourself.

Visible sewage or backing-up drains mean the line is blocked or failing, and the smell is the least of the problem.

1. Stop using water: no flushing, showers, laundry, or dishwasher.
2. Keep children and pets away, and don't touch sewage without gloves and boots.
3. Skip chemical drain cleaners. They can't reach a main line clog.
4. Call a drain pro for same-day service.

Typical cost: $100–$500 to snake the main line; $350–$1,400 for hydro jetting if the clog is severe or greasy

It's the most common cause and the cheapest one to fix: a drain that doesn't get used loses the water that blocks sewer gas.

1. Run water for a full minute in every sink, tub, and shower, and flush any unused toilets.
2. Pour about half a gallon of water into each floor drain.
3. Open a window or run the fan, then check again in an hour.
4. For a drain you rarely use, run water every couple of weeks, or ask a plumber about a trap primer.

Typical cost: Free if refilling the trap fixes it; $100–$250 for a plumber visit if the smell keeps coming back

A smell at the base of the toilet usually means the seal between the toilet and the floor drain has failed.

1. Gently push the toilet from side to side. Any movement suggests the seal has been broken.
2. Look for moisture, staining, or soft flooring around the base.
3. Have the toilet pulled and reset with a new wax ring. Caulking around the base won't fix a failed seal.

Typical cost: Usually $100–$250 for a plumber to reset the toilet and replace the wax ring

A drain you use every day has a full trap, so a smell there usually comes from buildup in the drain rather than sewer gas.

1. Pull the stopper or drain cover and remove any hair and sludge.
2. Scrub the drain and the sink's overflow hole with a long, narrow brush, then flush with hot water.
3. Check again the next day. If nothing has changed, come back and choose the option that fits.

Typical cost: Free to do yourself; $100–$250 if a plumber needs to clear the drain

If water from the faucet smells on its own, sewer gas isn't the problem and a drain repair won't fix it.

1. Compare the hot and cold water at a couple of faucets.
2. On city water, report the smell to your water utility.
3. On a private well, have the well serviced and the water tested.

Gurgling, or a smell that keeps returning after you refill the traps, suggests the plumbing isn't venting properly.

1. Refill the traps to clear the room in the meantime.
2. Note what sets it off, such as flushing, a certain drain, or windy weather. It helps a plumber find the problem faster.
3. Have a plumber check the vent. Leave the roof work to them.

Typical cost: $100–$250 for a plumber visit to diagnose it. Clearing a simple blockage is often part of that; opening a wall to repair a vent is quoted separately.

A smell that comes through the air vents can start at a dry condensate drain, and the HVAC system then spreads it around the house.

1. Find where the AC or dehumidifier drain line connects, and refill its trap if you can reach it.
2. Run water in any unused drains near the air handler.
3. If the smell continues, ask an HVAC pro or plumber to check for a dry drain or a leak near the return air.

Typical cost: Often free if a dry drain was the cause; $100–$250 for a plumber visit if it isn't

Full traps, no gurgling, and a smell that won't quit point to gas getting out somewhere you can't see.

1. Check that the cleanout caps in the basement, utility room, or garage are tight.
2. Write down where and when the smell is strongest.
3. Book a plumber or sewer pro for a smoke test or camera inspection.
4. Get a second repair quote that references what the inspection found.

Typical cost: $125–$500 for a camera inspection; line repairs are separate, commonly $1,100–$4,100

A sewage smell along with a wet, sunken, or extra-green patch suggests the buried line is leaking into the soil.

1. Keep cars off the area, and keep kids and pets away from it.
2. Book a camera inspection to find the location and depth of the break.
3. Get at least two repair bids that reference the camera footage.

Typical cost: $125–$500 for a camera inspection; $1,100–$4,100 for a repair; $3,000–$15,000 for a full replacement

A smell near the tank or field can mean the tank is due for pumping, a lid isn't sealing, or the drain field is struggling.

1. Don't open the tank lid yourself. Septic tanks can hold dangerous gases, and a fall in can be fatal.
2. Keep people and vehicles off any wet ground.
3. Find out when the tank was last pumped, and book an inspection.

A smell at a manhole or storm drain usually belongs to the public system, so the city should hear about it first.

1. Report the location to your sewer or public works department.
2. Stay out of any overflow, and keep kids and pets away from it.
3. Refill the traps in your house if you're smelling it indoors as well.

Plumbing vents release sewer gas above the roof by design, and on still days or in some winds it can drift down into the yard.

1. Note when it happens, including wind direction and time of day.
2. Walk the path of the sewer line and look for wet, sunken, or extra-green spots.
3. Ask a plumber about the vent if the smell becomes a regular problem.

Typical cost: $100–$250 for a plumber visit to take a look