Sewer Gas Smell in the House? Causes and How to Get Rid of It
A sewer or rotten-egg smell indoors usually means sewer gas is escaping past a barrier that’s supposed to block it — most often a dried-out P-trap in a rarely used drain, a failed toilet wax ring, or a venting problem. The fix is often simple (run water to refill a trap), but a persistent smell can point to a cracked pipe or vent issue that needs a plumber. And because sewer gas contains methane and hydrogen sulfide, a strong, lingering smell shouldn’t be ignored. Here’s how to track it down.
First: Rule Out a Natural Gas Leak
Natural gas and sewer gas both smell like rotten eggs/sulfur. If the smell is strong and sudden, treat it as a possible natural gas leak first: leave the house and call your gas company from outside. Once gas is ruled out, work the sewer-gas causes below.
Common Causes
| Cause | Why it smells | Fix |
|---|---|---|
| Dry P-trap | The water seal that blocks gas evaporated (unused sink/floor drain) | Run water / pour water down the drain |
| Failed toilet wax ring | Seal between toilet and flange leaks gas | Reset toilet, new wax ring |
| Blocked/broken vent stack | Roof vent can’t equalize pressure, gas backs in | Plumber clears/repairs vent |
| Cracked drain pipe | Gas escapes from a damaged line | Pipe repair |
| Clogged drain / buildup | Decaying gunk in the drain | Clean drain |
| Loose cleanout cap | Open access point | Cap it |
The Easy Wins (Try These First)
- Run water in every drain — sinks, tubs, floor drains, the basement, guest bathrooms. A dry P-trap is the #1 cause and refilling the water seal fixes it instantly.
- Check rarely used fixtures — a floor drain or spare bathroom that hasn’t seen water in weeks.
- Pour water (and a little oil) into floor-drain traps that evaporate fast.
- Inspect around the toilet base — rocking, water, or smell points to the wax ring.
- Clean the affected drain of buildup.
When to Call a Plumber
If the smell persists after refilling traps and resetting toilets, the cause is likely venting or a damaged pipe — not DIY territory. A plumber can smoke-test the system to find leaks, inspect the vent stack, and camera the line. A whole-house or recurring smell can overlap with a main sewer line clog or backup.
| Work | Typical cost |
|---|---|
| Toilet reset + wax ring | $150 – $350 |
| Drain cleaning | $150 – $400 |
| Vent stack repair/clearing | $200 – $600+ |
| Smoke test / camera inspection | $150 – $500 |
If a quote seems high, see plumber quote seems high.
Is Sewer Gas Dangerous?
In small amounts it’s mostly a nuisance, but sewer gas contains hydrogen sulfide and methane. High concentrations can be a health hazard and methane is flammable, so a strong, persistent smell warrants prompt attention — ventilate and get a plumber.
Frequently Asked Questions
Why does my house smell like sewer gas? The most common cause is a dried-out P-trap in a rarely used drain — the water seal that blocks sewer gas evaporated. Other causes include a failed toilet wax ring, a blocked or broken vent stack, a cracked drain pipe, or buildup in a drain. Start by running water in every drain to refill the traps.
How do I get rid of a sewer smell in the house? First run water in all sinks, tubs, and floor drains to refill dry P-traps, which fixes most cases. Check around toilet bases for a failed wax ring, clean smelly drains, and cap any open cleanouts. If the smell persists, call a plumber to check the vent stack and look for cracked pipes.
Is sewer gas in the house dangerous? Small amounts are mainly an unpleasant nuisance, but sewer gas contains hydrogen sulfide and methane. High concentrations can cause symptoms and methane is flammable, so a strong or persistent smell shouldn’t be ignored — ventilate the area and get the source fixed. Also rule out a natural gas leak, which smells similar.
What is a P-trap and why does it dry out? A P-trap is the U-shaped bend under drains that holds a small water seal to block sewer gas from coming up the pipe. In fixtures that aren’t used for weeks — guest bathrooms, floor drains — that water evaporates, breaking the seal and letting gas in. Running water refills it; a little mineral oil slows evaporation in floor drains.
Why does the sewer smell come and go? Intermittent smells often track with usage and weather: a trap that dries between uses, wind affecting the vent stack, or pressure changes pulling gas in when water drains. Persistent or worsening smells, especially whole-house, more likely indicate a venting problem or a cracked pipe that needs a plumber to diagnose.
Last updated: June 16, 2026. Sources: EPA indoor air and sewer gas guidance; standard plumbing P-trap and venting diagnosis; 2026 cost ranges per our plumbing guides. Strong rotten-egg smell = rule out a natural gas leak first.