Bathroom Smells of Sewage | Five Checks Before You Call

Sewage smell in a bathroom is one of those things that sets people straight onto Google looking for emergency drain unblocking. Sometimes that's the right call. Often, though, the drain is absolutely fine and the smell is coming from somewhere much simpler and cheaper to fix yourself.

Before you pay anyone, run through these checks. Most take under five minutes and need nothing more than a torch and a jug of water.

Check 1: The Dry Trap Under a Rarely Used Basin or Shower

Every waste fitting, basin, shower tray, bath, has a U-bend beneath it. That U-bend holds a small body of water that physically blocks sewer gas from rising up into the room. The water is called the trap seal.

If a fitting doesn't get used for a week or two, evaporation empties that trap. No water, no seal. Sewer gas drifts straight up and you're standing there wondering if you've got a collapsed pipe.

This is extremely common in Exmouth holiday lets at Sandy Bay and in second bathrooms in larger houses on the Halsdon and Hulham estates, anywhere a basin or shower tray goes unused for stretches.

The check: Pour about half a litre of water straight down every plughole in the room. Add a tablespoon of vegetable oil to each one. The oil sits on the water surface and slows evaporation. Wait ten minutes and see if the smell goes. If it does, that was your problem. Done.

Check 2: The Toilet Wax Seal (or Pan-to-Soil-Pipe Joint)

At the base of every toilet there's a seal where the pan connects to the soil pipe. Traditionally wax, sometimes a rubber push-fit ring. When that seal deteriorates, sewer gas escapes at floor level, spreads around the room, and gets stronger whenever someone flushes.

You won't necessarily see water. A failed seal doesn't always leak, it just lets gas past.

The check: Rock the toilet pan gently front to back and side to side. Any movement at all? That's a sign the fixing bolts or the seal have given up. Also crouch down with a torch and look at the joint between the pan base and the floor. Any dark staining, discolouration, or soft-looking grout around there? Get the pan off and reseal it. It's a straightforward job for a plumber, not a drainage engineer, and it doesn't involve digging anything up.

Check 3: The Soil Vent Stack

The soil vent stack is the large-diameter pipe, usually 110mm, that runs vertically from your drains up through or alongside the house and terminates above the roofline. Its job is to vent sewer gases safely up and out. If the top is blocked, cracked, or if the pipe itself has a hairline crack somewhere in the run, gas gets pushed into the building instead of escaping to atmosphere.

Older houses in Lympstone, Topsham, and the Victorian terraces around Exmouth Seafront often have cast iron stacks that are getting on for a century old. Cast iron corrodes from the inside. A pipe can look fine from outside and be substantially compromised inside.

The check: Go outside and look at the top of the stack. Is there a mesh cage or a cap on it? Bird nests block these vents faster than anything. If you can safely see the top, check for obvious obstruction. Inside, a cracked stack sometimes shows as a damp streak on a wall, a patch of paint bubbling, or just a persistent smell in an upstairs room that has no basin or toilet of its own. A CCTV survey of the stack will confirm a crack quickly and without opening any walls.

Check 4: The Inspection Chamber or Manhole Cover You've Forgotten About

Some bathroom smells aren't actually coming from inside the bathroom at all. They're coming in through a gap, an ill-fitting skirting board, a cable entry point, a service void, from a manhole or inspection chamber that's either cracked or has a lid that doesn't seat properly.

Lift every manhole cover near the house. A smell rising from one of them doesn't mean there's a blockage. It can mean the chamber itself has a cracked benching, or the channels inside are silted up and harbouring a build-up of gases.

The check: On a still day, lift the lid, stand back, and let it air for a minute. Foul smell from the chamber that disappears when you move away from the house suggests the chamber, not an internal fitting, is the source. Replace any lid that rocks or doesn't sit flat. A badly seated lid lets gas rise at ground level, and if your house has a chamber near a back door or a low vent tile, it gets drawn in.

Check 5: The P-Trap on the Bath

Baths are the worst offenders for a subtle one. The trap is deep under the bath, usually accessed via a panel, and it collects hair, soap, and general debris. Over time, the decomposing material in the trap itself produces a smell independent of the main drain. It can also partially block the trap and reduce the water seal depth.

The check: Take the bath panel off. With a torch, look at the trap. Is there visible build-up around the trap body? Unscrew the trap access cap if there is one and clear it out. Then run the bath for a minute to refresh the trap seal. That decomposing debris smell is often mistaken for a sewer gas problem. It's not, it's a cleaning problem.

When It Actually Is a Drain Problem

If you've worked through all five checks and the smell persists, or if you're also seeing slow drainage, gurgling from multiple fittings, or any sign of sewage backing up, then yes, something further down the system needs looking at. A CCTV drain survey will tell you whether it's a partial blockage, a displaced joint, or a root intrusion without anyone guessing.

The thing to resist is going straight to "we need to dig it up". A liner or a patch repair fixes a huge proportion of cracked or displaced joints without breaking a single slab.

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Drainsco covers Exmouth and the surrounding EX postcodes. Engineers are available 24 hours a day, seven days a week. There's no call-out fee, and you'll get a clear price before any work starts. If you've run through the checks above and still can't trace the source, a CCTV survey is usually the fastest way to settle it.