What causes a sewer gas smell in the house?

The most common causes are a dried-out P-trap in a rarely used drain, a failed toilet wax ring, a blocked or faulty vent stack, or a cracked or loose drain line. Each lets gas escape the waste system into the home. This is different from a sewage backup, where wastewater physically comes up into the house. Tracing it usually starts with the simplest causes first.

How do I get rid of a dried P-trap smell?

Run water down every drain, including floor drains and any fixture that is rarely used, for about a minute to refill the trap with its water seal. If the smell fades over the next day, a dry trap was likely the cause. If it returns or never fades, the source is probably elsewhere, such as a wax ring, vent, or cracked line.

Do you fix the plumbing that causes sewer gas?

No. The plumbing repair, refilling or fixing traps, replacing a wax ring, clearing a vent, or repairing a cracked line, is handled by a licensed plumber. Our role is odor removal. Once the plumbing fault is sealed, we clear the residual sewer gas smell that has soaked into nearby materials and the air using green, non-toxic methods.

Will the smell go away on its own after the leak is fixed?

Sometimes a mild odor clears once the source is sealed and the area is aired out. But sewer gas often soaks into drywall, subfloor, cabinetry, and soft furnishings, and that residual smell can linger. We remove it with thermal fogging, hydroxyl generators, HEPA and activated-carbon scrubbing, and sealing where needed, all green and non-toxic, never ozone or masking.

How to Find and Remove a Sewer Gas Smell in Your House

Specialty · By Odor Removal Experts · Updated June 2026 · Cleveland and Northeast Ohio

That rotten egg or sour drain smell drifting through a bathroom or basement is almost always sewer gas, and it is telling you something about your plumbing. This is different from a flooded sewage backup, where wastewater has physically come up into the home. Sewer gas is the odor escaping from your drain and waste system through a gap that should be sealed, often a dried-out trap or a failed seal somewhere in the line. The smell can be unpleasant and, in larger amounts, genuinely worth addressing promptly.

The good news is that sewer gas problems are usually traceable. In this guide we will walk through the common sources, a dried P-trap, a failed wax ring, a vent stack issue, and a cracked or loose line, how to narrow down which one you are dealing with, and how the residual odor gets cleared once the plumbing side is corrected. Some of this you can check yourself. For the harder finds and the leftover smell, that is where a pro comes in.

The short answer

A sewer gas smell almost always means your plumbing has a gap letting odor escape, usually a dried-out P-trap, a failed toilet wax ring, a blocked vent stack, or a cracked drain line. Start by running water down every drain to refill the traps. A plumber seals the leak, then we clear the residual odor with green methods.

Sewer gas usually means a dried trap, wax ring, vent, or cracked line.
Start with the simplest fix: refill every trap with water.
A plumber seals the leak; we clear the residual smell afterward.
Green methods only, never ozone or masking.

What sewer gas is and where it comes from

Your plumbing is designed to keep sewer gas out of the house through two features working together. Water-filled traps, the curved P-traps under sinks, tubs, and floor drains, hold a small plug of water that blocks gas from rising back up the drain. Vent pipes, which run up through the roof, let the system breathe so that water flows without siphoning those traps dry. When either part fails, gas finds its way in.

The classic smell is a rotten egg or sulfur odor, sometimes more of a stale, sour drain smell. It often shows up in a bathroom, a basement, a laundry area, or near a rarely used fixture. Heat and humidity can make it stronger, and you may notice it more when the house has been closed up.

Because the smell travels on air currents, the spot where you smell it strongest is not always exactly where it is escaping. That is why a systematic check beats guessing.

The common sources and how to spot them

Some sources you can rule out yourself; the hidden ones usually need a plumber. Here are the common causes and how each tends to show up.

Dried-out P-trap: the most common and the easiest to rule out. If a sink, tub, floor drain, or basement drain has not been used in a while, the trap water evaporates and lets gas straight through. Running water down every drain for a minute refills the traps, and if the smell fades over the next day, that was likely it.
Failed toilet wax ring: if the seal under a toilet has worn or the toilet rocks slightly, gas can escape around the base, often with the smell strongest right at floor level near the toilet.
Vent stack problem: a blockage from leaves or a nest, a disconnected vent, or one that is too short can cause traps to siphon dry repeatedly or push gas into the home.
Cracked or loose drain line: sometimes inside a wall or under a floor, it can leak gas where you cannot see it.

You can check the simple things, refilling traps, looking for a rocking toilet, listening for gurgling drains. The hidden sources, vents and cracked lines, usually call for a plumber to locate and repair the plumbing fault itself.

Fix the plumbing first, then clear the odor

Sewer gas is a plumbing issue at the source, so the leak path has to be corrected first. Refill or repair the trap, replace the wax ring, clear or fix the vent, or repair the cracked line, depending on what the inspection turns up.

Seal the source before treating odor

Until that gap is sealed, any odor work is temporary, because new gas keeps coming in. A licensed plumber handles the structural repair side of this.

Once the source is sealed, there is often a residual smell that has soaked into nearby porous materials, drywall, subfloor, cabinetry, or that is lingering in the air and any soft furnishings. That leftover odor does not always clear on its own, which is where our work comes in.

We remove the residual odor with green, non-toxic methods. Thermal fogging neutralizes smell that has set into pores and gaps. Hydroxyl generators, safe in occupied spaces, break down the lingering odor compounds. HEPA and activated-carbon scrubbing pulls the rest from the air, and we seal any surface that still holds smell. We never use ozone or chlorine and never just mask it.

When to call a pro

If you have refilled the traps, checked for a rocking toilet, and the smell still persists, or if it is strong and you cannot pin down the source, it is time to bring in help. A plumber finds and fixes the plumbing fault, and we clear the odor that remains afterward. A persistent sewer gas smell is also worth taking seriously, so do not let it drag on.

Most odor removal jobs we do are completed in one to four hours, and we offer same-day or next-day service in most cases. We are fully insured and back the work with a 100 percent guarantee. If the smell is not gone, we are not done.