Where do cockroaches in the bathroom come from? Usually from drains and the sewer network, especially when the U-bend (trap) is dry or the drain has no tight cover. The bathroom has everything a cockroach needs: water, humidity, darkness and gaps around pipes.
How cockroaches get into the bathroom
- Floor drain: the most common entry, especially in rarely used bathrooms, because the water in the trap dries out and opens a path from the sewer.
- Pipe gaps: the space around sink, toilet and water heater pipes inside the wall.
- Extractor fan and light well: cockroaches travel through shafts and ducts between flats.
- Under the bathroom door from the rest of the house.
- Bath and shower drains without a strainer.
Which cockroaches appear in bathrooms?
- American cockroach (large): usually comes from the sewer and emerges from the drain at night. See American Cockroach.
- German cockroach (small): lives inside the home behind bathroom cabinets and around pipes, and likes damp warmth. See German Cockroaches.
The rule: if the cockroaches are large and come out of the drain, the problem is the drainage. If they are small and numerous, the problem is inside the home itself.
How to stop cockroaches coming out of drains
- Keep the trap full of water: pour water into every drain once a week, especially in closed bathrooms.
- Fit a tight drain cover or a one-way valve cover that lets water down and stops insects coming up.
- Seal gaps around pipes with silicone or filler.
- Fit fine mesh over the extractor fan opening outside.
- Fix leaks and let the bathroom dry after use.
How to get rid of cockroaches already in the bathroom
- Apply cockroach gel in small dots around sink pipes, behind the toilet and inside the bathroom cabinet.
- Spray a residual insecticide around the drain from outside, and in manholes, roof and yard drains.
- Apply dust into gaps around pipes inside the wall before sealing them.
- Do not spray over the gel, so cockroaches are not driven away from it.
- Monitor with glue traps for two weeks.
If cockroaches are appearing all over the house, not just the bathroom, see Why Cockroaches Appear at Home.
Products from Orkida
- Advion cockroach gel by Syngenta
- Demand CS by Syngenta
- Maxforce Forte gel
- K-Othrine Partix by Envu (formerly Bayer)
- K-Othrine dust
Bathroom cockroach FAQs
Do cockroaches come up through the toilet?
Rarely. The toilet always holds water in its trap, making it hard for a cockroach to come through. The usual entry is the floor drain.
Does bleach in the drain stop cockroaches?
It kills what it reaches and cleans, but it does not stop them coming up in the long run. The solution is a full trap and a tight cover.
Why do cockroaches come out at night?
Because cockroaches are active in the dark, and the quiet of night lets them come out for food and water.