Bathroom Smells of Sewage | Five Checks Before You Call

A sewage smell in the bathroom is one of those problems that gets worse the more you ignore it. Not because it's always serious, but because people assume it's a blocked drain, call someone out, and spend money on a job that wasn't the issue. Sometimes the fix is a jug of water and thirty seconds of your time.

Here's how to work through the likely causes yourself before anyone touches a spade.

Why this matters before you call a drainage company

Sewage smells have a handful of common causes, and a blocked drain is only one of them. Most of the others don't need jetting, CCTV, or any kind of remedial work. They need you to look at something specific for five minutes.

Work through these in order. The first three cost nothing.

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Check 1: The dry trap (most likely cause, easiest fix)

Every waste fitting in your bathroom, your basin, your bath, your shower tray, has a U-shaped section of pipe underneath called a trap. That U holds a small plug of water that physically blocks sewer gases from rising back into the room.

If a fitting hasn't been used in a while, the water evaporates. No water, no seal. Sewer gas comes straight up.

This is the number one cause of bathroom sewage smells, particularly in: - En-suites that are only used occasionally - Guest bathrooms in properties on Franklands Village, Bolnore Village, or anywhere with a second bathroom that sits empty most of the week - Basins that were plumbed in but are rarely used day to day

What to do: Run every tap, flush the shower, and use every fitting for thirty seconds. Fill each trap back up. Then wait twenty minutes and smell again. If the smell goes, you've found it.

If the smell comes back within a day or two, the trap itself may have a fault, a capillary leak, or an incorrectly sized dip that drains itself. That's a plumber job, not a drainage job.

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Check 2: The toilet wax seal (or rubber gasket)

At the base of your toilet pan, where it meets the floor and connects to the soil pipe below, there's a seal. Traditionally wax, though newer installations often use a rubber compression fitting. Either way, it's not immortal.

When it fails, sewer gas leaks up around the base of the toilet. The smell can be quite strong, and it tends to be worse in warm weather when gases expand.

Signs the seal has gone: - Slight movement in the toilet pan when you sit on it - Discolouration or staining at the base - Smell that's stronger right next to the toilet than anywhere else

What to do: Kneel down and push gently on the pan near the base. Any rocking at all is a red flag. Smell the floor immediately around the toilet base. If it's noticeably worse there, the seal is the first thing a plumber should replace before anything else is investigated.

This is a straightforward plumbing repair, not a drainage emergency. Don't let anyone tell you they need to survey the drain to diagnose a rocking toilet pan.

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Check 3: The soil vent stack (easy to overlook, surprisingly common)

Your soil stack is the large vertical pipe, usually 100mm or 110mm diameter, that carries waste from toilets and waste fittings down to the drain at ground level. It also vents upward through the roof. That upward vent is critical. It lets air in to balance pressure, which stops the siphoning effect that would otherwise pull water out of your traps.

If the vent at the top is blocked, partially blocked, or the stack itself has a crack, things go wrong in two different ways:

1. A blocked vent cap causes negative pressure in the stack. That negative pressure sucks water out of your traps, which brings us back to Check 1, except topping up the traps doesn't fix it for long because they drain again.
2. A cracked stack lets gas escape into the void between your internal wall or floor and the living space. You smell sewage but can't pin it to any specific fitting.

What to do: Go outside and look at where the soil stack exits through the roof. You're looking for a vent cap, sometimes called a vent cowl. Is it intact? Is there a bird nest or debris visible? Inside, if your stack runs against an internal wall, press your hand gently against the wall near the stack run. Any smell coming from the wall surface itself suggests a crack.

A cracked stack needs a CCTV survey and either a patch repair or, if the crack is significant, a section of relining. It's not a dig-it-up situation in most cases.

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Check 4: The inspection chamber or gulley near the house

Step outside and lift the nearest drain cover. A few things to look for:

• Standing water above the invert level (the bottom of the channel) suggests a partial blockage or restricted flow downstream
• Sludge or greasy deposits on the chamber walls
• A smell from the chamber itself that's extreme, more than a normal drain smell

If the chamber looks normal and flows freely when you run a tap inside, the smell is almost certainly coming from one of the internal causes above, not from outside.

If you can't lift the cover yourself, or there isn't a visible chamber on your property, that's fine. Just note whether the external drains seem relevant before you call.

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Check 5: Recent building or plumbing work

Has anyone worked on your bathrooms or drainage in the last six months? A new basin fitted without checking the trap depth, a soil pipe re-run that wasn't properly supported, a rubber seal disturbed during tiling. These are all real scenarios.

In Lindfield and Cuckfield especially, where older housing stock gets a lot of renovation work, a poorly fitted waste fitting is behind more unexplained smells than people realise.

If work has been done recently, go back to whoever did it before calling a drainage company. If the trap or seal was disturbed during their job, that's their responsibility to fix.

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When you do need a drainage engineer

If you've worked through the above and the smell persists, it's time for a CCTV drain survey. Not because the drain is definitely blocked, but because a camera is the only way to rule out:

• A cracked or root-damaged section of the underground drain
• A partial collapse causing slow drainage and gas build-up
• A failed connection between the soil stack and the underground drain

A good engineer will show you the footage. If nothing is found underground, at least you know the problem is internal and you can go back to a plumber with confidence.

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Drainsco covers Haywards Heath and across the RH16 and RH17 postcodes, with engineers available around the clock. There's no call-out fee, and we'll give you a clear price before any work starts. If you've worked through the checks above and still can't pin the smell down, a camera survey is usually the next sensible step. Give us a call and we'll talk it through.