That rotten-egg, sewage smell is sewer gas finding its way into your home — usually through a dry trap, a venting problem, or a drain issue. Here is how to track down the source and fix it.
Written bySteven Lockhart·Reviewed byMiguel Lopez, Owner & Licensed Plumber (CSLB #974600)·Last reviewedJune 2026 · 5 min read
Quick Answer
A sewer smell in the house is sewer gas escaping into living space, most often because a drain trap has dried out (letting gas up an unused drain), a vent is blocked, or there is a drain or wax-ring problem. The fix depends on the source: refill a dry trap, clear a vent, or repair the leak. Persistent or strong sewer gas should be checked, since at high concentrations it can be hazardous. This is part of our complete guide to drain cleaning in West Los Angeles.
Asking why does my house smell like sewage usually comes down to a broken seal. Every drain has a U-shaped trap that holds water to block sewer gas, and the plumbing is vented through the roof so gas escapes outside. When a trap dries out, a vent clogs, or a seal fails, that gas comes inside instead. The good news is the most common cause — a dry trap in a rarely used drain — is the easiest to fix. This guide is part of our complete resource on drain cleaning in West Los Angeles.
Sewer odor is the smell of sewer gas (often hydrogen sulfide, the rotten-egg odor) entering the home when a drain trap, vent, or seal fails to keep it in the drainage system.
The right sewer gas smell fix depends on where it comes from, and a rotten egg smell in a drain points to specific causes. The table maps where and when you smell it to the likely source.
| Where/when you smell it | Likely source | The fix |
|---|---|---|
| Near a rarely used drain | Dried-out trap | Run water to refill the trap |
| Whole bathroom, worse over time | Failed toilet wax ring | Reset toilet, new wax ring |
| Smell plus slow drains | Drain/vent blockage | Clear the line or vent |
| Outside near roof/walls | Blocked or broken vent | Clear/repair the vent stack |
Sewer odor in the bathroom most often comes from a guest shower or floor drain whose trap has dried out, or from a toilet whose wax ring seal has failed and is letting gas (and sometimes water) escape at the base. Run water in unused drains first; if the smell is strongest around the toilet base or it rocks slightly, the wax ring is the likely culprit and the toilet should be reset. If neither solves it, the odor is coming from the drain or vent system and we will trace it.
A homeowner has a persistent sewage smell in a guest bathroom that air freshener never fixes.
New Pro finds the seldom-used shower trap had dried out and the toilet wax ring was failing, letting gas in at the base.
Refilling the trap and resetting the toilet with a new seal removes the odor at its source — no masking required.
The Bottom Line
A sewer smell indoors is sewer gas slipping past a trap, vent, or seal — not something to cover with air freshener. Start by running water in unused drains; if it persists, the cause is in the vent or drain system and worth tracing. Call any time and we will find and fix the source. More on our drain cleaning page.
Sewer gas is getting past the barriers that normally block it — most often a drain trap that has dried out, but also a blocked vent, a failed toilet wax ring, or a drain problem. Finding which one is the key to fixing it.
If it is a rarely used drain, run water to refill the trap — that solves the most common case. If the smell persists, it points to a vent blockage, a failed seal, or a drain issue that should be traced and repaired.
Sewer gas is mostly unpleasant at low levels, but it contains hydrogen sulfide and other gases that can be hazardous at high concentrations. A strong or persistent smell should be investigated promptly rather than ignored or masked.
Often a dried-out trap in a seldom-used shower or floor drain, which lets gas up when the water seal evaporates. Running water periodically keeps the trap full. If it is constant, a seal or vent issue is more likely.
Yes. A failed wax ring lets sewer gas escape at the toilet's base, sometimes with slight rocking or water seepage. Resetting the toilet with a new seal usually resolves it.
Then the odor is coming from the drain or vent system — a blockage, a cracked pipe, or a venting fault. That needs tracing with the right tools, which we can do, often with a camera inspection.
Written by the New Pro Plumbing content team and reviewed for technical accuracy by Miguel Lopez, owner and California-licensed plumber (CSLB #974600). Pipe lifespans are presented as typical ranges, not guarantees, and any pricing is confirmed in writing before work begins.
What's new: June 2026 — first publication.
We trace sewer odor to its source — trap, vent, or line — and fix the cause. Call any time.
