As you may have learned from the Smoke Test FAQ, knowing that there's a problem in the Sanitary Sewer System--a fault, flaw or defect that allows additional inflow into the system--is one thing. Finding it is something else! One method of locating flaws is the smoke test, in which non-toxic smoke is introduced into the system and technicians carefully monitor where the smoke emerges from the ground. Frequently, however, the smoke seems to vanish and doesn't emerge at all, or it emerges somewhere on private property--your residence, for example! This is where a Building Survey comes in. Often the only way to identify a flaw in the sanitary sewer system is to physically inspect a dwelling to determine where the defect is.