Why Does My Bathroom Smell Like Sewage?

Sewer gas gets into a bathroom one way almost every time, around the water seal, the bit of water parked in the bend under each drain. When your bathroom smells like sewage, that seal has been beaten by a dry P-trap, a wax ring that gave up under the toilet, a blocked vent, slime in the drain or the overflow hole, or a basement floor drain nobody’s fed since spring. With a flashlight you can rule most of them out in ten minutes on your knees.

Find the Source: Sink, Shower, Toilet or Floor Drain

Gas is strongest within about a foot of where it gets out. A sewer smell in bathroom air that’s faint at the mirror and ugly at the drain hole belongs to the sink.

Toilets are easier, since the tank up top smells of nothing. If the toilet smells like sewage around the base, you’re kneeling inches from the leak. A shower drain smells like sewage mostly after it’s been left alone, say over a long weekend in Saugatuck. And with every drain upstairs clean, head down to the basement, where plumbers find the sewer gas smell in house after house coming from a floor drain nobody remembers.

A Dry P-Trap: The Fix That Costs Nothing

The guest bathroom in a Chicago bungalow gets used at Thanksgiving and then forgotten. Under its sink sits a U-bend, the P-trap, and the water in that bend, the trap seal, is the whole barrier between the room and the sewer. Nobody touches the unused shower while the radiators run hot all winter, and by the time your sister visits in February the water’s gone.

A pitcher fixes the dry P trap smell, the cheapest repair in this article. Pour in a quart and the room’s fine within the hour. If your bathroom smells like sewage again a week later, that trap’s dropping water faster than any radiator explains, and something under the sink is leaking.

A Failed Wax Ring or a Rocking Toilet

The toilet sits on a ring of wax, squashed flat between the porcelain and the toilet flange in the floor, with two closet bolts holding everything still. Wax is a one-time seal. After a few hundred wobbles the ring flattens on one side, and that side is where the gas walks out.

Sitting down tells you plenty. A rocking toilet tilts or clicks when you lean toward the paper holder, and in a two-flat the upstairs owner hears about it from the brown ring on the downstairs ceiling.

Tight closet bolts buy a few months of quiet. The ring itself gets replaced with the toilet off the floor, which is a job for our toilet repair crew.

Gurgling Drains and a Blocked Vent

Drains need air the way a juice box needs that second hole, and they get it from the vent stack running up through the roof. A bird’s nest or a January ice cap closes it off, and falling water then pulls air out of your traps.

Pulling the plug on a full tub is the test. If the sink beside it gurgles while the tub empties, that gurgling drain is losing its trap, and a slow drain that burps air belongs to the same story.

The roof part stays off your list. A flat Chicago roof in November is near the top of the repairs you should not DIY in Chicago, and a plumber clears a plumbing vent with a cable from above.

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Buildup in the Drain and the Overflow Hole

Hair and soap scum wrap around the drain stopper. Bacteria move into that mess and coat it in biofilm, a slime that smells like a sewer even though it’s mostly your own shampoo.

The overflow hole near the rim of a sink is worse, since water hardly ever reaches it. Put your nose to it and you’ll know in a second.

Ten minutes on a Saturday morning does it. The stopper comes out for a wipe, then a bottle brush and hot soapy water go into the drain and the overflow. Drain chemicals stay at the store, since they pour straight past the slime.

Chicago Basements: Floor Drains and Combined Sewers

Most sewers around Chicago are combined, according to the MWRD guide to how Chicago sewers work. What you flush and the rain off your street share one pipe. Your house joins that combined sewer through a private lateral, which is yours, while the street sewer is the city’s.

Picture a July storm outrunning the street sewer. The water climbs back to the lowest opening, a basement floor drain, and you’ve got a basement backup. A clogged or broken lateral gives you the same sewer backup on a dry day.

The Deep Tunnel, TARP, holds 11.5 billion gallons. Before it, by the 1960s, the sewers overflowed about 100 days a year, and 38.8% of Chicago’s housing went up before 1940.

A sewer smell in basement units with a dry floor is the trap again, and a floor drain smell in a garden unit or basement bathroom leaves with one bucket. For backups, MWRD points to a check valve or an overhead sewer.

Is Sewer Gas Dangerous?

The CDC ToxFAQs on hydrogen sulfide call it a colorless, flammable gas with a rotten egg smell, and people notice it at 0.0005 to 0.3 ppm.

The numbers get ugly further up. Weeks spent around 10 ppm or less leave people with sore eyes and headaches, and they’re tired all the time. At 100 ppm the nose can quit noticing the stuff, while 500 ppm knocks people out cold without warning.

Get a headache or a dizzy spell in a stinking bathroom and the move is outside, windows thrown open behind you for ventilation. A strong rotten egg smell with nausea gets a 911 call from the porch.

When to Call a Plumber

A plumber with a drain camera earns the fee once you see any of these.

• The smell’s back a day after you refilled every trap.
• Any toilet that rocks when you sit, damp floor or not.
• Every drain in the place gurgling at once, which puts the vent or the main line in the frame.
• If water shows up on the basement floor after a storm, the lateral’s the suspect.

Our licensed plumbers do drain cleaning in Chicago and drain pipe repair, plus the rest of our plumbing services in Chicago, on a 30-day workmanship warranty.