Why Does My House Smell Like Sewage? 6 Causes (And How to Fix the Smell)

A sewage or rotten-egg smell in the house is one of those problems you can’t ignore and can’t quite locate. It comes and goes, it’s strongest near a drain or in one room, and it’s genuinely unpleasant. The smell is sewer gas — and while a faint, occasional whiff is usually a simple fix, a persistent one can point to a real plumbing or septic issue.

Here’s what causes it, ranked from “you can probably fix it yourself” to “call someone,” and how to track it down.

First, a Quick Word on Why It Matters

Sewer gas is mostly methane and hydrogen sulfide (that’s the rotten-egg smell). In small amounts it’s just foul; in large amounts it’s a health hazard and, with methane, a fire risk. So it’s worth chasing down — not just masking with an air freshener.

The 6 Causes

1. A Dried-Out P-Trap (The Most Common Cause)

Every drain has a U-shaped pipe beneath it called a P-trap, which holds a little water that seals out sewer gas. In a sink, shower, or floor drain that hasn’t been used in a while — a guest bath, a basement floor drain, a laundry sink — that water evaporates, breaking the seal and letting gas up.

The fix: Run water down the drain for a minute to refill the trap. For a floor drain that dries out often, pour in a cup of water (and a splash of mineral oil to slow evaporation) every few weeks. Free.

2. A Clogged or Blocked Vent Stack

Your plumbing has vent pipes running up through the roof that let sewer gas escape outside and let drains flow smoothly. If a vent gets blocked — leaves, a bird’s nest, debris — gas backs up into the house and drains gurgle or run slow.

Signs to look for: Gurgling drains, slow drainage throughout the house, and smell near multiple fixtures.

The fix: Clearing the vent stack from the roof. $150–$400, and not a DIY job if you’re not comfortable on the roof.

3. A Loose or Failed Toilet Seal

The wax ring under your toilet seals it to the drain. When it dries out, cracks, or the toilet rocks loose, sewer gas escapes around the base — often with a smell that’s strongest right at the toilet.

Signs to look for: Smell concentrated around one toilet, a toilet that rocks, or occasional water at the base.

The fix: Resealing the toilet with a new wax ring. $150–$300.

4. Dirty or Clogged Drains

Buildup of grease, hair, soap, and food in the drain and pipes can rot and smell on its own, separate from sewer gas. A kitchen sink that smells is often this. (Worth knowing what not to pour down your drains to prevent it.)

The fix: Cleaning the drain — sometimes a thorough flush, sometimes professional drain cleaning or hydro-jetting for stubborn buildup.

5. A Cracked or Broken Sewer/Drain Line

A damaged pipe under the house or in a wall leaks sewer gas (and sometimes water) into the structure. This smell is persistent, doesn’t track to any one fixture, and may come with damp spots or signs of a backup.

The fix: A camera inspection to find the break, then a repair. Costs vary widely with location and severity.

6. Septic Problems

If you’re on septic, a sewage smell — inside near drains or outside over the yard — can mean a tank that’s overdue for pumping or a failing drain field. An outdoor sewage smell near the tank or field is a classic warning sign.

The fix: If the tank’s full, pumping solves it. If the field’s failing, that’s a bigger job — watch for the other warning signs of a failing septic system.

How to Track It Down

Work from easy to hard:

1. Run water in every drain, including ones you rarely use, to refill dried traps. Wait a day — if the smell’s gone, that was it.
2. Check around the base of every toilet for a smell or any rocking.
3. Note whether the smell is one spot or everywhere. One spot points to a trap, toilet, or drain. Everywhere points to a vent, a line break, or septic.
4. Check outside near the septic tank and drain field if you’re on septic.
5. If it persists after the easy checks, call — a vent, line, or septic issue needs a pro.

Frequently Asked Questions

Is a sewer gas smell dangerous? A faint, occasional whiff usually isn’t harmful, but persistent or strong sewer gas can cause headaches and nausea and, with methane, poses a fire risk. Don’t just mask it — find the source.

Why does my bathroom smell like sewage only sometimes? That’s the classic sign of a dried-out P-trap in a fixture you don’t use often, or a venting issue that worsens with wind or weather. Running water down the drain is the first thing to try.

Why does my house smell like sewage outside near the yard? On a septic system, an outdoor sewage smell often means an overdue tank or a failing drain field. It’s worth getting checked before it becomes a backup.

Can I just pour bleach down the drain to kill the smell? It might mask a dirty-drain smell briefly, but it won’t fix a dried trap, a vent block, a bad toilet seal, or a septic issue — and bleach can harm a septic system. Find the real cause.

How much does it cost to fix a sewage smell near Canton, GA? It ranges from free (refilling a trap) to $150–$400 for a vent or toilet reseal, up to more for a line or septic repair. We diagnose the source first so you’re not paying to fix the wrong thing.

Can’t Find Where the Smell Is Coming From? We Can.

If you’ve refilled the traps and checked the toilets and your house still smells like sewage, the cause is likely a vent, a line, or your septic system — and that needs proper diagnosis. Precision Plumbing & Septic will track down the source, including running a camera if needed, and fix it at the root. Because we do both plumbing and septic, we can follow the smell wherever it leads.

Call (678) 758-3493 — Cody answers the phone himself. We’re available 24/7 with a 60-minute emergency response across Cherokee, Cobb, and North Fulton, serving Canton, Woodstock, Holly Springs, Ball Ground, Acworth, Alpharetta, Roswell, Kennesaw, Cumming, and the surrounding North Georgia communities.