A smoke test is a sewer inspection method whereby nontoxic smoke is forced into sewer system access points. The smoke makes its way through all connected pipes in sewer system, thereby indicating pipe leaks, breached utility holes, cracks, uncapped lines, and other defects. Testers can also locate unknown pipe sections, such as cleanouts, downspouts, and sump pumps. Certain types of connections may contravene local ordinances.
Regarding the smoke itself, the City of Oakland explains:
“The smoke is nontoxic and nonhazardous and is manufactured specifically for this purpose. It leaves no residuals or stains, and has no effects on plants or animals. The smoke should not enter your home, but if it does, it will have a distinct odor and should only last a few minutes with proper ventilation. Please note, all plumbing fixture drain traps must be filled with water prior to smoke testing.”
Homeowners are requested to pour water down all drains of plumbing fixtures in order to fill the P-traps. This helps prevent smoke from entering the house.
During the smoke test, you may see smoke coming out of grass, utility boxes, cracked pavement, or elsewhere. Each test typically lasts about 15 minutes. Homeowners do not need to be home during testing, although it can be helpful to ensure the home is well-ventilated in case smoke enters the home. Alert the testing crew immediately if smoke appears inside your house.