A sewage smell inside your house comes from one of two places. Either the plumbing is letting gas in through a dry trap or a bad vent, or the septic system is backing up or failing to drain. Where you smell it, when, and what else is going on usually tell you which.
A faint smell near one drain is rarely urgent. A strong smell, a smell with headaches or dizziness, or sewage coming up through a drain is.
Do this first
- If the smell is strong or anyone feels sick, get out. Open windows on your way, leave the house, and call the fire department. That’s Wisconsin’s health department advice for high levels of sewer gas indoors.
- Run water into every drain you rarely use, including floor drains, basement showers and guest bathroom sinks.
- Check the septic alarm panel if your system has a pump.
- Cut back on water if drains are slow or gurgling, until you know what’s wrong.
Don’t open the septic tank or a riser lid to look, and don’t pour cleaners or deodorizers down the drain to cover the smell.
Why sewer gas deserves attention
Sewer gas is a mix of gases that forms as waste breaks down. Wisconsin’s Department of Health Services lists hydrogen sulfide and ammonia among the toxic ones, along with methane and carbon dioxide. Hydrogen sulfide is the rotten-egg smell.
At low levels, Wisconsin lists eye and respiratory irritation, dizziness, drowsiness, headaches and nausea. At high levels, the gas can cause unconsciousness and death, and methane is flammable and explosive.
The Illinois Department of Public Health adds a warning. At higher levels, your nose can be overwhelmed and you can’t smell it. A smell that fades isn’t always a smell that’s gone.
If you have symptoms and suspect sewer gas, Wisconsin’s advice is to see a doctor.
Where and when you smell it
| Where and when | Likely cause | What to do now | Read more |
|---|---|---|---|
| One drain, often one that’s rarely used | Dry trap | Run water into it and see if the smell clears | This page |
| Near the house, worse on calm days or in a cold snap | Blocked or frozen roof vent | Have a plumber check the vent | Yard smells like sewage |
| Every drain, with gurgling or slow drainage | Tank full, blocked line or failing drain field | Cut water use and call a septic professional | Toilet gurgling |
| After heavy rain, fading as things dry out | Drain field struggling to take water | Cut water use and watch the yard | Drain field failure |
| With the septic alarm on | Pump chamber not emptying | Cut water use and call for service | Septic alarm going off |
| Indoors and outdoors, with wet spots in the yard | Drain field failing | Keep people off the wet area and call | Drain field failure |
| Pumping is overdue or you don’t know the date | Tank too full | Book a pump-out and inspection | How often to pump |
Sewer smell in house drains: the plumbing causes
Start with these. They’re cheaper, and you can rule some of them out yourself.
A dry trap
Every drain has a trap, the curved section of pipe that holds a little water. That water seals the sewer gas out of the room. When a drain sits unused, the water evaporates and the gas comes straight up.
The Illinois Department of Public Health says drains with dry traps can let hydrogen sulfide into the home. The University of Nebraska-Lincoln also lists traps not filled with water among the causes of indoor sewage odors.
To confirm it, run water into the suspect drain. If the smell fades over the next day, you’ve found it. Wisconsin’s health department suggests flushing floor and sink drains with water regularly so the traps don’t dry out.
A blocked or frozen vent
Your plumbing vents through a pipe on the roof. The EPA says these vents can get clogged with leaves and debris, or freeze shut during long cold spells. If you’re in Minnesota, Wisconsin or New England, keep the freezing part in mind every winter.
A blocked vent often shows up as gurgling first, which toilet gurgling explains. According to the EPA, a vent may need cleaning or raising, and charcoal filters for roof vents can help with the smell.
Wisconsin suggests checking the roof vent for leaves or bird nests now and then. Leave the ladder to a plumber, though.
Other plumbing openings
The University of Nebraska-Lincoln’s list also includes improper plumbing and venting in the house and an unsealed wastewater ejector sump pump. Wisconsin adds cracks in the foundation, where gases in the soil next to the house can get in.
These take a plumber to diagnose, once the traps and vent are ruled out.
The septic causes
If the smell comes with symptoms elsewhere in the system, look outside the house. The EPA says that if your drain field isn’t working properly, you may smell an odor inside your home as well as around the system. Cornell Cooperative Extension makes the same point, noting that odors around the house can come from a septic drainage problem or from the plumbing vents.
The tank is too full
A tank that’s overdue for pumping is the first septic suspect to rule out. Signs your tank needs pumping covers what to look for. If you don’t know when it was last pumped, how often to pump helps you work out if you’re overdue.
A damaged baffle
The EPA describes the T-shaped outlet in the tank as the part that keeps sludge and scum from leaving the tank and traveling to the drain field. When it’s damaged, solids can reach the field. Septic tank baffles explains the damage, and only a professional with the tank open can confirm it.
A backup
Cornell describes dark, foul-smelling sewage backing up into drains or toilets as a symptom of failure, and the EPA lists wastewater backing up into household drains among the signs to call a professional about. If you see sewage in a drain, stop using water and call.
A drain field that can’t keep up
Slow drains throughout the house, gurgling, and wet or spongy ground over the field point here. The EPA lists bright green, spongy grass over the drain field in dry weather, and pooling water around the system, as signs of failure. Drain field failure walks through what’s recoverable and what isn’t, and yard smells like sewage covers the outdoor side.
A pump that has stopped
On systems with a pump chamber, an alarm usually sounds first. When the septic alarm goes off covers the first steps.
What you can safely check yourself
- Run water into drains you rarely use, including floor drains.
- Look at the alarm panel, if you have one.
- Walk the yard for wet spots, strong smells or unusually green strips over the field.
- Find the date of your last pump-out.
What you leave alone matters just as much. Never open the septic tank or a riser, and never lean over an open one. Septic gases can kill, and a lid can give way. Don’t pour bleach, drain cleaner or scented products down the drain to mask the smell, either. The EPA warns that toxins poured down the drain can kill the organisms that treat your waste, and what not to flush has the details. And stay off the roof.
When to call a professional
Call right away if:
- The smell is strong or lasts after you’ve filled the traps
- Anyone in the house has headaches, dizziness or nausea
- Sewage is backing up into a drain or toilet
- There are wet spots or standing water over the tank or drain field
- The septic alarm is on
Call a plumber for a smell at one drain or near the vent that water doesn’t fix. Call a septic professional for anything that comes with slow drains, backups, wet spots or an alarm. The EPA also suggests contacting your local health department when a system is malfunctioning.
What it’s likely to cost
A dry trap costs nothing but a bucket of water. A vent repair or a pump-out sits at the lower end of plumbing and septic work, and septic tank pumping costs covers that bill.
A failing drain field is the expensive end. Drain field replacement costs covers what that involves.
How to keep it from coming back
- Run water into rarely used drains every so often, as Wisconsin’s health department suggests.
- Have the system inspected regularly. The EPA recommends at least every three years for a typical household system.
- Pump on schedule, so the tank never gets close to full.
- Keep chemicals and grease out of the drains.
- Have the roof vent checked if you get odors on calm days or after a hard freeze.
Common questions
How do I get rid of the sewer smell in my house?
Find the source first. Run water into rarely used drains to refill dry traps, which is the simplest fix. If that doesn’t work, have a plumber check the vent, and call a septic professional if the smell comes with slow drains, backups or wet spots in the yard. Covering the smell with products doesn’t fix it.
Is sewer smell in a house toxic?
It can be. Wisconsin’s health department lists eye and respiratory irritation, dizziness, drowsiness, headaches and nausea at lower levels of hydrogen sulfide, and unconsciousness or death at high levels. Illinois lists similar effects. Wisconsin’s advice is to see a doctor if you have symptoms, and to leave and call the fire department if you think the gas is concentrated indoors.
Is it safe to sleep in a house with sewer gas?
None of the health departments here addresses sleeping specifically. Wisconsin’s advice is to leave and call the fire department if you think sewer gas is concentrated indoors, and to see a doctor if you have symptoms. Illinois warns that at higher levels you may stop smelling the gas at all, so a fading smell doesn’t prove it’s gone. Until the source is found and fixed, don’t assume the smell is harmless.
Why does my house smell like sewage but no leak?
Sewer gas doesn’t need a leak you can see. A dry trap, a blocked roof vent, an unsealed ejector pump or a crack in the foundation can all let it in, and a drain field that isn’t working can cause an odor inside too.
Sources
- Wisconsin Department of Health Services, Sewer Gas
- Illinois Department of Public Health, Hydrogen Sulfide Gas
- US EPA, Resolving Septic System Malfunctions
- US EPA, A Homeowner’s Guide to Septic Systems
- University of Nebraska-Lincoln Water, Troubleshooting Septic Systems
- Cornell Cooperative Extension, Your Septic System: Septic System Failure