Smoke testing is a method of locating leaks in sewer & drain plumbing systems. This approach is typically used when foul sewer gas odors are present, both inside or outside of a building or home. Roberts Plumbing Hydro Jet & Rooter uses a product called SAFE SMOKE. It is actually a vapor and not smoke. This product is the safest on the market and odor free . This is the same product that many fire departments use nationally for their smoke training programs. Smoke testing is becoming more and more popular as it helps avoid busting open walls just on a hunch.