TL;DR
A sewage smell in the bathroom nearly always means sewer gas is escaping where it should not. There are four usual causes: a dry trap, a blocked vent, a cracked pipe or a build-up of biofilm inside the pipe. Because the smell alone will not tell you which one you have, work through the checks below first. If it does not clear, request a free quote online.
A dry trap
Every sink, shower and floor drain has a trap, which is the U-shaped bend under the fitting. It holds a little water that blocks sewer gas from reaching the room. In a bathroom that is rarely used, that water can dry out and break the seal.
This is the easiest cause to spot and fix. The smell is often worst first thing in the morning, and it eases after you run the tap for a few seconds. However, if the smell returns within a day, that fixture is drying out faster than it should. Mention it when you book a bathroom plumbing visit.
A blocked or faulty vent stack
The vent stack is a pipe that runs up through the building and out above the roof. It lets air into the drains so water flows freely. If leaves, debris or a crack block that pipe, the system cannot breathe properly. As a result, water can get pulled out of nearby traps.
The tell-tale sign is gurgling from more than one drain, such as the toilet gurgling while the shower runs. In older converted buildings in Hollingdean area and across Brighton, several flats may share one original vent. A fault on one floor can therefore show up as a smell in the flat above or below. Because the vent ends above the roof, most people should leave this check to an engineer.
A cracked or damaged pipe
Waste and soil pipes can crack with age, ground movement, frost or building work. A crack upstream of the vent gives gas a way out before it reaches fresh air. That means you can smell sewage even when every trap in the room holds water.
This cause is harder to spot from the smell alone. Look for damp patches on a nearby wall or ceiling, new mould, or a smell with no clear pattern. Finding the exact point usually needs a CCTV drain survey, because the damage could sit anywhere along the pipe. Our guide to what a CCTV drain survey shows explains how that works.
Biofilm and organic build-up
Inside almost every drain, a thin layer of soap scum, hair and other residue builds up over time. As it breaks down, it can smell very like sewage, although the trap, vent and pipe are all fine. The smell is usually strongest at the plughole or overflow, and drainage may be slow.
Unlike a dry trap, running more water does not shift this smell, since the source coats the pipe wall. Proper clearance with jetting or a drain auger works better than a bottle of shop-bought cleaner. For a slow shower as well as a smell, see our advice on unblocking a shower or bathroom drain. We also help households in Southwick area with this kind of problem.
Finding the actual cause
All four causes can produce a similar smell, and more than one can happen at once. Treating the wrong one wastes time. For example, topping up a trap does nothing if a pipe is cracked further along.
A camera survey shows whether a trap holds water, whether the vent is clear, and whether there is a crack or a build-up. Once you know, you can book the right fix with some confidence. If you also have a blocked drain symptom, read our overview of blocked drain causes in Brighton and Hove. A smell after rain in a lower flat may link to the points in our piece on basement flat drainage. Costs depend on the property, so read how CCTV survey pricing works before you ask for a quote. Then request a free quote online and we will help narrow it down in Brighton area.
Frequently Asked Questions
Why does my bathroom only smell sometimes? An on-and-off smell often points to a dry trap that fills again when you run the tap. It can also mean a vent problem that only shows when several fixtures run together. A constant smell is more likely a cracked pipe or biofilm.
Will bleach or drain cleaner get rid of the smell? It might hide a biofilm smell for a short time. However, it will not fix a dry trap, a blocked vent or a cracked pipe. Harsh chemicals also do older pipework no favours, so find the cause instead.
Is a sewage smell dangerous? Sewer gas is unpleasant, and it contains small amounts of substances you would rather not breathe. Open a window and get the cause checked rather than living with it. If anyone feels unwell, get fresh air and seek medical advice.
Why does only one of my two bathrooms smell? That is a useful clue. It suggests the cause is local to that room's trap, vent connection or pipe run, not the whole property.
