What is worrying you: a smell you can't place

A smell you can't place: yard, drain or gas

A sewer smell in the yard can mean a failing septic system or a leaking sewer line, so note where it is strongest and leave every lid shut¹. If it could be gas or propane, leave the house first and make your calls from outside².

Start at the back door and walk the yard slowly, staying on the grass and off any lids.

Updated November 4, 2026, Midlands House Walk

A gas or propane smell comes before everything else on this page. Get everyone out, without touching a switch or using a phone inside. Once outside, call 911 and the gas company or propane supplier².

Long open strip of tall green grass running through pine woods — Tall green grass over a septic drain field in pine woods. Lush grass and a smell together are worth a call to a septic contractor.

Band of darker, taller grass with a trace of standing water across a pale lawn — A soggy strip of greener grass in a paler lawn. Put a smell beside a patch like this, and the septic field moves to the top of the list. AI-generated picture.

Greener or soggier grass

Look for: Clemson’s failure signs include greener grass over the field, a dead grass outline and soggy areas, along with odors¹.
What it tells you: A smell plus any of these points toward the septic system. The soggy patch stop helps you sort septic from pipe from rain.

Old iron waste stack behind a cut opening in a wall next to a timber stud — Cast-iron drain pipes behind an opened wall. A sewer smell indoors usually starts at a drain, or at a pipe like these.

Indoors, near a drain

Look for: If it could be gas, even a rotten-egg smell, leave the house first and call from outside; gas companies add that odor so leaks get noticed. Only when you’re sure it’s a drain smell, note which room it’s strongest in. Run water down any drain nobody uses, because a dry trap lets sewer air through.
What it tells you: Slow drains along with the smell are another of Clemson’s signs¹. Sewage coming up a drain needs different steps, and quickly.

White water heater in a round pan inside a hall closet, louvered door open — A tank water heater in a hallway closet, standing in a drain pan. A closet like this can trap a smell, so if it seems like gas, leave the house. AI-generated picture.

Near the water heater

Look for: If it smells at all like gas, skip this check and leave. Otherwise, note whether the smell seems to come from this closet, and don’t open panels or touch the heater.
What it tells you: The water heater stop says what to look at on an ordinary day. A smell of gas or propane here isn’t an ordinary day, so read the warning on this page.

Concrete tank with two round lids sitting in a freshly dug hole — A concrete septic tank with two round lids, set in a fresh hole in Quebec, Canada. Yours is buried like this, and it stays closed.

What stays closed

Look for: Look at the ground around a lid for sagging or wet spots, from where you stand, and don’t go any closer.
What it tells you: Don’t lean over a tank: fumes can cause fainting, a flame nearby can cause an explosion, and old tanks can collapse¹.

What if it's coming from next door?

Clemson says failing systems are reported to the regional environmental office, and a complaint can lead to a violation under Reg 61-56¹. Septic now sits with SC DES, though Clemson’s pages may still say DHEC. A friendly word over the fence may be the first step. There’s more on septic care.

Yours to do

Note where the smell is strongest, what time, and whether rain just fell.
Ease off heavy water use during or just after rain³.
On city sewer, report sewage on the ground right away, with your address or cross streets⁴.

For a licensed pro

Licensed septic contractors do inspections, repairs and pump-outs. Clemson says owners shouldn’t inspect a tank themselves⁵.
A plumber for drains, traps and sewer lines inside the house.
The gas company or propane supplier for any gas smell.