What a Sewer Smoke Test Finds, and When to Book One

A sewer smell in the basement. A floor drain that gurgles. A stripe of lawn that is greener than the rest. None of these tells you where the problem is. They only tell you something is wrong. A smoke test is one way a plumber finds the where, without digging up the yard first. DB Plumbing now offers smoke testing on sewer systems, and here is what that means for you as a homeowner.

How a smoke test works

The idea is simple. The plumber seals off a section of the sewer system, then pushes visible smoke through the pipes with a blower. Smoke follows any path it can find. If the system is sound, the smoke stays inside the pipes and leaves only where it is meant to, usually through the vents on the roof. If there is a crack, a break or an opening where there should not be one, smoke rises out of the ground, a cleanout or a spot inside the house, and shows exactly where the problem is.

That is the part people like. A problem you cannot see underground becomes a plume you can point at. Instead of guessing which stretch of pipe to dig up, you know. DB Plumbing describes it as finding the problem without guesswork, and that is a fair summary of what the test is for.

What it can find

DB Plumbing lists four things a smoke test is good at:

• Sewer odors. If you smell sewer gas indoors or out in the yard, smoke shows where the gas is getting out.
• Cracks, breaks and hidden openings in sewer lines, found without invasive digging. A line can be damaged for a long time before anything shows at the surface.
• Improper connections. A drain, vent or storm connection tied in where it should not be shows itself when smoke appears somewhere unexpected.
• System integrity. A clean test is information too. If the smoke stays where it belongs, you have good evidence the system is holding together.

The storm connection is worth a word. When rain water from a gutter or a yard drain ends up in a sewer line, it puts water in the system that was never meant to be there. You may never notice it from inside the house. A smoke test can reveal it, which is hard to do any other way short of tracing every pipe by hand.

Not every smell means a broken pipe

Before you book anything, it helps to rule out the simple causes. Every drain has a trap, the curved section of pipe that holds a little water and blocks gas from rising. A floor drain in a corner of the basement that rarely sees water can dry out, and a dry trap lets gas straight up. Pour a few quarts of water down it and see whether the smell goes away.

If the smell comes back, or you cannot find a dry trap, the problem is somewhere less obvious. That is when a smoke test earns its place. It separates a nuisance from a real break, and it does it without turning your lawn into a trench.

When to book a smoke test

• You smell sewer gas inside the house or near the foundation, and it comes and goes.
• Drains slow down or back up again soon after being cleaned.
• A patch of lawn is soft, sunken or unusually green along the path of the sewer line.
• You are buying or selling a home and want to know how the sewer system is doing.
• A renovation or landscaping project will put digging or weight over a line you have never inspected.
• A cleaning did not explain the problem, and you want an answer rather than another guess.

Ground conditions and the season can change how easy it is to see smoke leaving the pipes, so ask about timing for your property when you call.

What to expect on the day

A smoke test is quicker and less disruptive than excavation. Expect the plumber to ask you to run water in any drain that does not get much use, so the traps are full and smoke does not drift into the house. Ask whether anything else needs doing ahead of time, since the details depend on your property and your plumbing.

One small courtesy: smoke rising out of a lawn can alarm a neighbor who does not know why. A quick heads-up saves a phone call.

What happens after the test

If the test comes back clean, you have ruled out the sewer line itself, and the search for your problem can move somewhere else. If smoke shows an opening, you know where the repair is needed, and the repair can be aimed at that spot rather than at a whole run of pipe. That is the practical value. You pay attention to the right place, whether the answer is a repair, a connection that needs correcting or nothing at all.

If a sewer smell or a mystery drain problem has been bothering you, the sewer smoke testing page on this site explains what DB Plumbing offers, and the drain and sewer page covers the repairs that can follow. To ask about booking, call DB Plumbing in Brainerd at (218) 851-3424, Monday to Friday, 8 to 5.