During smoke testing, field crews force smoke into the sanitary sewer. During these tests, the possibility exists for smoke to enter a residence or business due to infrequently used drains or a defect in the private property sewer pipes.
A drain trap is the S-shaped curvature or elbow in the pipe that exists to capture and hold water in the trap's curve. This water in the trap creates a type of seal and blocks gases from rising up through the drain and into the home. This trap will also keep the smoke from entering the building. A dry drain trap could be found in drains which are not used regularly and the water has evaporated.
Water should be ran in these isolated areas monthly to maintain the drain seal in proper operating condition.
If smoke testing is taking place in your area, you should check to see that all drain traps under basins, washing facilities and floor drains contain water; simply flush toilets and run or pour water into all drains, including unused fixtures and floor drains.