Entry pointsModerate risk
Can Cockroaches Come Through Drains?
Quick answer
Yes. Large cockroaches, especially American cockroaches, live in sewers and stormwater systems and can climb up through floor wastes, shower drains and unused sinks. A drain’s water trap (the U-bend) normally blocks them, but traps that dry out, damaged grates and gaps around pipes give cockroaches a direct route inside.
Why this happens
Sewer and stormwater pipes are warm, humid and full of organic matter, which is ideal cockroach habitat. The American cockroach in particular is closely associated with sewers.
Plumbing traps hold a small amount of water that blocks sewer gases and insects. In rarely used showers, laundry floor wastes, guest bathrooms and holiday homes, this water evaporates and leaves an open path. Cockroaches can also squeeze through damaged or missing grates and gaps where pipes pass through floors and walls.
Activity through drains tends to increase on hot, humid nights and after heavy rain, when water levels in stormwater systems rise.
What you may be seeing
- Large, reddish-brown cockroaches in bathrooms, laundries or showers, often at night.
- Cockroaches appearing near floor wastes rather than near food.
- A sewer smell from a drain, which suggests the trap is dry.
What you can do
- Run water into every drain at least once a week, including floor wastes and spare bathrooms.
- Make sure every drain has an intact, well-fitted grate; replace damaged ones.
- Seal gaps around pipes where they enter walls and floors.
- Use drain plugs or covers in drains that are rarely used.
- If you notice persistent sewer smells, ask a licensed plumber to check the traps and vents.
What not to do
- Do not pour insecticides or household chemicals down drains; they can harm waterways and are not a label-approved use for most products.
- Do not assume one cockroach from a drain means an infestation inside the house.
If you use any insecticide or bait, read the label first and follow it exactly. Australian law requires products to be used only as the label directs, including where and how they may be applied and how to protect children and pets.
When professional help may be needed
If cockroaches keep appearing from drains after traps are kept wet and grates are fixed, there may be a plumbing defect, and a plumber may be the right first call. Pest professionals can treat around drains, sub-floors and entry points where label directions allow.
Related pest
Species mentioned
American Cockroach
Periplaneta americana
One of the largest household cockroaches in Australia. Lives in drains, sewers and sub-floors and wanders inside on warm nights.
Oriental Cockroach
Blatta orientalis
A dark, glossy cockroach that prefers cool, damp places such as drains and basements. Less common in Australian homes than other large species.
Related questions
Related guides
The Australian Guide to Cockroaches
Everything an Australian household needs to know about cockroaches: which species you are seeing, why they are there, how they get in, the health implications, and how to prevent and manage them.
GuideHow to Pest-Proof Your Home
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GuidePest Prevention Checklist
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GuideUnderstanding Pest Activity After Rain
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GuideCommon Brisbane Household Pests
A Brisbane-specific overview of the pests residents meet most often, when they are active, and what the subtropical climate, storms, creeks and Queenslander homes mean for pest pressure.
GuidePests in Queenslander Homes
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Local information
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Sources & further reading
- Australian Museum — insects and spiders — Australian Museum
- Queensland Museum — insects, spiders and animals of Queensland — Queensland Museum
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