Bad smell from a sink, shower or floor drain, or a sewage smell in the house? The usual causes, simple checks you can try and when you need a drain engineer.
By AJ, certified Gas Safe engineer and lead plumber at 247 Emergency Plumbers Edinburgh · Checked
A drain smell usually comes from a dry trap in a sink or shower that is rarely used, or from food, grease and hair rotting in the pipe. Running the tap or cleaning the trap often fixes it. A sewage smell that keeps coming back, or appears with slow drains, can mean a blockage further down and needs a drain engineer.
Water near electrics? Do not touch wet switches, sockets or light fittings. Switch off at the consumer unit only if you can reach it without standing in water. Water pouring in? Turn off the stopcock: find your stopcock →
What it could be and what to do
Dry trap You may be able to fix this
Likely cause: The water in the U-bend stops sewer gas coming up. HomeServe says it can dry out in sinks or showers that are rarely used.
What to do: Run the tap for a minute in every sink, shower and bath that is not used often.
Build-up in the trap You may be able to fix this
Likely cause: HomeServe says food, grease, hair and soap stick in the drain and bacteria growing on them cause much of the smell.
What to do: Put a bowl underneath, unscrew the trap under the sink by hand and clean it out. Keep grease and food out of the sink.
Blocked drain or vent Engineer needed
Likely cause: A blockage further down, or a blocked vent pipe, pushes smells back into the house. Slow drains or gurgling with the smell point this way.
What to do: If more than one sink drains slowly, or the smell is outside near a drain cover, call a drain engineer.
Smell keeps coming back Engineer needed
Likely cause: A failed seal on a toilet or a cracked pipe can leak sewer gas.
What to do: Call us. A CCTV drain survey can find where the smell is coming from.
Safe checks you can do first
These are the checks we suggest before a plumber arrives. Stop if anything feels unsafe.
Stop the water: use the small isolation valve on the pipe to the fitting if there is one, or the main stopcock, usually under the kitchen sink. Stopcock finder →
Electrics: keep away from anything wet and electrical. Get an electrician to check before switching back on.
Is it just you? Ask neighbours. No water or brown water in the whole street is usually Scottish Water: 0800 0778 778, free, 24 hours.
Contain it: buckets, towels and moving belongings limit the damage. In a flat, warn the neighbour below.
Photos: take photos and video before you clear up, for your insurer or landlord.
Need a plumber now? Call us any time.
Our callout is from £75 in standard hours (out of hours £100–£180) for attendance and diagnosis. Drain unblocking labour is £70–£180. Any repair and parts are agreed with you before work starts.
Our emergency line is open 24 hours a day, 7 days a week.
Every property is different. This page is general guidance, not a diagnosis.
YOUR QUESTIONS, ANSWERED
Helpful answers before you call.
Why does my sink smell like sewage?
Usually the water in the trap has dried out, or food and grease are rotting in it. Run the tap and clean the trap. If the smell comes back with slow drains, there may be a blockage further down.
Should I pour boiling water down a smelly drain?
We do not recommend it. Many waste pipes are plastic and boiling water can soften joints. Hot tap water and cleaning the trap are safer.
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