Large numbers of cockroaches could inhabit city sewer mains, which provide a favorable environment complete with food, shelter and abundant moisture. Cockroaches travel from building to building along the damp surfaces of hidden pipes as well as inside sewer pipes. Floor drains provide a convenient entry point for cockroaches, according to extension specialist Peggy K. Powell of West Virginia University.
Water traps in drains place several inches of water between the interior of the sewer system and the living area of the home. Outside vents allow air to enter the drainage pipes as toilets flush and pass unpleasant sewer gases to the outside of the building. Water traps block the passage of most insects, but cockroaches can find their way through. Swimming ability varies, but some cockroach species can swim underwater at full speed for two minutes and survive quiet submergence for 15 minutes, according to Eugene Garfield of the Institute for Scientific Information.
Buildings connected to municipal sewer systems stand greater chances of cockroach invasions through drainpipes. Independent septic systems operate as sealed chambers protected against insect infestations by several feet of earth. Bathtub and sink drains could admit cockroaches, but cockroaches found in sinks and tubs probably entered from above. Damp environments caused by sweating pipes or fixtures attract cockroaches already living in the building. Floor-level drain openings connecting to larger drainpipes in basements give cockroaches better access to buildings. Installing a fine mesh wire screen under the sieve plate of floor drains traps cockroaches and their nymphs inside the pipe, says the West Virginia University Extension.
Wire mesh drain covers shaped to fit tub and sink openings block the drainpipes but also clog easily and require frequent cleaning or replacement. Many other parts of the home or apartment offer more likely entry points for cockroaches and should also receive attention. Any gap along basement walls or foundations gives cockroaches shelter and a route into the home. Gaps around pipes where plumbing passes through walls also give cockroaches access to the home. Sealing all gaps and cracks with caulking compound keeps roaches out. Cockroaches feed on grease, soap and food scraps accumulating in dirty drains. Cleaning drains regularly makes drain traps less attractive.
Glue traps won't eliminate cockroaches but do give homeowners a simple way to check for problems. Glue traps in crawl spaces, basement corners and beneath sinks in kitchens and bathrooms catch a sampling of the cockroach population in sticky adhesive. If trapping indicates a problem, homeowners could hire professional exterminators or act on their own. Boric acid sprayed into crevices where cockroaches hide poisons the insects. Diatomaceous earth contains sharp particles that damage the cockroach's carapace and cause death by dehydration. Both approaches leave cockroach bodies behind. Dust created when cockroaches decay could cause asthmatic reactions in some people.