Sewer smell in the bathroom: how to find the cause and fix it
Photo : Fructibus · CC0 1.0
Updated 2026-10-26
A sewer smell in the bathroom is unpleasant, but the cause is almost always easy to find. Most of the time, a drain trap has dried out or become dirty. Sometimes the problem is a toilet seal, the ventilation of the waste stack, or the public network backing up after heavy rain. This is a common issue for holiday homes and properties owned by people living abroad, which can stay closed for months. Here is how to find the source yourself, what you can do without tools, and when to call a plumber (plombier in French, bloumbi in Darija).
Why does it smell like sewage?
Every drain (basin, shower, bath, toilet, floor drain) has a trap that holds a little water. That water acts as a plug that stops sewer gases from coming up. When the water disappears or the trap stops working, the smell enters the room.
- Dry trap: water evaporates in a rarely used bathroom, a guest room, or a flat left closed for months
- Floor drain (siphon de sol): found in most Moroccan bathrooms, it dries out quickly if no water reaches it and clogs with hair and soap
- Dirty trap: hair, soap and limescale deposits that ferment
- Damaged toilet seal: a hidden leak at the toilet outlet, often with a stain or smell at the base of the bowl
- Siphoned trap: when you flush, a nearby trap empties (gurgling sound). This usually means the waste stack is not properly vented
- Overloaded network: after heavy rain, the public sewer or septic tank can back up and the smell rises through low points
Find the source in 10 minutes
Close the door, wait a few minutes, then smell each drain up close. Note when the smell appears: all the time, after a shower, after flushing, or only after rain.
- Pour one to two litres of water into every drain, especially the floor drain. If the smell fades quickly, the trap was dry
- Flush and listen: gurgling in the shower or basin means siphoning
- Look at the base of the toilet: blackened seal, damp or a loose tile
- Check under the basin: a loose trap or a waste pipe that has slipped out of its joint
- Don't forget the washing machine: a dirty filter or drain hose can smell too
What you can do yourself
Many smells disappear with simple maintenance. Building-product manufacturers recommend these steps:
- Top up rarely used traps regularly. Before leaving a property for a long time, a little oil on top of the trap water slows evaporation
- Unscrew and rinse the basin trap, with a bucket underneath
- Clean the grate and basket of the floor drain
- Pour in a spoonful of baking soda, then a glass of white vinegar, wait half an hour and rinse with very hot water
- Avoid harsh chemical drain cleaners, especially if water is standing: they can damage PVC pipes
- Never pour cooking oil or flush wipes down the drains
When to call a plumber
If the smell keeps coming back after cleaning, the cause is deeper and you need a professional.
- Constant smell at the base of the toilet: the seal or connection needs redoing, sometimes by removing the bowl
- Traps empty every time you flush: the stack has no vent or a blocked one, common in houses built without a plumbing plan
- Smell throughout the home or in several rooms: a broken inspection chamber or pipe, or a full septic tank in areas not connected to the sewer
- Dirty water rising through the floor drain after rain: a non-return valve (clapet anti-retour) may be recommended
- In an apartment building, if several neighbours notice the same smell: it is the shared stack, to be handled with the syndic
How much does it cost?
There is no official rate. Cleaning or replacing a trap is a small call-out, often charged as a flat fee. A Moroccan construction-pricing site recorded a plumber's day rate of roughly 300 to 550 MAD in 2026, with prices varying by city and urgency. Re-venting a stack, replacing a buried pipe or a camera inspection is priced by quote. Always ask what is included (parts, travel) before the plumber starts.
Find a plumber with AloAji
On aloaji.ma, search for "plombier" and your city to see plumbers near you. Call or WhatsApp them directly, free. Describe the problem (which drain, when the smell appears) and send a photo so they can give you a first idea of the price. Profiles marked "Non vérifié" are businesses found on their own websites that AloAji has not checked yet.
FAQ
Why does my bathroom smell like sewage even though it's clean?
Most often a trap has dried out, especially the floor drain or a shower that is rarely used. Pour in one to two litres of water: if the smell goes away, that was the cause.
The smell appears when I flush. Why?
Flushing pulls water out of nearby traps, letting gases through. It usually means the waste stack is not properly vented, which a plumber should check.
It smells worse after rain. Is that normal?
Heavy rain can overload the public sewer or septic tank, and the smell rises through low points such as the floor drain. If dirty water comes up, a plumber may suggest a non-return valve.
How do I stop smells in a flat that stays closed for months?
Before leaving, fill every trap and add a little oil on top to slow evaporation. When you come back, run water in every tap and drain for a few seconds.
How much does a plumber charge for a sewer smell in Morocco?
Cleaning or replacing a trap is a small flat-fee job. Work on the stack or pipes is quoted. As a reference, a plumber's day costs roughly 300 to 550 MAD depending on the city.