Don’t (Always)  Blame the Installer

Odor problems in facilities with onsite treatment systems often can be traced to issues outside the installer’s responsibility
Don’t (Always)  Blame the Installer
The test equipment: a handheld leaf blower connected to the inlet pipe of the septic tank, a rock to help deflect wind to help the smoke get into the blower, and a 30-second smoke bomb. (Photos courtesy of Russ Lanoie)

When there’s a sewage odor at a home or other building with a septic system, the tendency is to blame the onsite installer first.

But odors can have causes well outside the installer’s control. So when an odor problem arises and you are called to investigate, be prepared to do a little detective work. It could help save your reputation and help the owner find the real source of the trouble.


Persistent smell

Just a few years ago our community of Mount Washington Valley, N.H., built a beautiful new nature learning center — a stunning structure that produces its own power, heats itself mainly by the sun, has its own septic system. As a regular volunteer at the center, I heard the staff complain about a persistent foul odor in the building, thought to be coming from the septic system.

As luck would have it, one day when I happened to be at the center, the plumbing backed up into the building. Acting quickly because there were several school kids in programs at the building, I located and uncovered the septic tank and found a 90-degree elbow installed at the inlet pipe, sending septage down below the level of the water in the tank. I removed the elbow, and the pipe cleared itself.

I was told that the original site contractor had installed this elbow after hearing about the odor problem, in an effort to stop sewer gas from backing up into the building. This did not solve the problem, and it created another one.

I had seen many 50- to 75-year-old systems installed with an elbow at this location instead of the tee that we use as an inlet baffle to allow sewer gases to vent through the plumbing to the building’s “stink pipe” and out through the roof. It’s possible that this down-facing elbow was originally intended not to serve as an inlet baffle but to block odor for older plumbing that often was not vented as well as modern plumbing.


Simple smoke test

Thinking the problem might be odor from the roof vent finding its way back down and in through open windows, I supplied a charcoal filter for the vent pipe. This provided little relief, so I suggested that a plumber check all the toilet seals to be sure they were secure – a leaky toilet seal can easily let odor into a building without leaking any water.

Just after an experienced plumber reset each of the toilets, the center had a well-attended activity accompanied by a lot of bathroom use. I was told the next day that the smell was “enough to gag a maggot.” So I set out to determine just where the odor might be coming from by doing a crude but effective smoke test.

This technique involves the use of a few pipe fittings, a leaf blower, and a smoke bomb from a plumbing supply store — the same type of smoke bomb that heating system installers use to test the integrity of their hot-air distribution systems.

In this case, I used a 90-degree elbow attached to the inlet pipe, pointed up and out of the tank, connected to another 90-degree elbow and reduced by a rubber connector to the discharge of the leaf blower. By setting the smoke bomb next to the air intake of the running blower, I was able to pressurize the plumbing system with smoke, in hopes of seeing just where odor might be getting into the building.


The real culprit

Almost immediately we could tell that the house vent was clear because the charcoal filter spewed white smoke as if we had just elected a new Pope. We also got a lot of smoke in the men’s room — enough to set off the fire alarm system that is directly connected to the local fire department, whose representatives soon arrived.

When I showed the photo of the smoke billowing out from behind the urinal to the firemen, they were as astonished as we were. The problem stemmed from the seal between the urinal and the wall flange — it had slipped out of position as the urinal was installed. It never allowed any water to leak, but the odor took its toll on the staff for four years before we diagnosed the problem.

I was confident from the start that the septic system could not be the problem, but it took the smoke test to prove it. And aside from the cost of running the fire truck up to the center, the whole test cost only a few bucks.


How you can do it

Here are a couple of things to consider if you do this sort of smoke test to prove that a smell is not your septic system’s fault. I used a 30-second smoke bomb that sells for about $6. Start with at least a couple so that you can learn by trial and error.

Since I already had the leaf blower, I saved the cost of a professional smoke test unit that sells for well over $1,000. A shop vacuum discharge hose probably would have worked just as well. I simply aimed the smoke bomb discharge (out the side of the device) toward the blower.

But be forewarned: Start the blower and warm it up before hooking it up to the sewer pipe connections. If you start the blower cold when it is already hooked up, the high idle of the cold engine will be enough to blow the water out of some of the plumbing traps. While it’s easy to refill the traps, it takes a little mopping to clean up the water from the floor and walls.

If possible, disarm the fire alarm system in case your test is as successful as ours was — unless you have a good working relationship with your local folks in red trucks.

About the author

Russ Lanoie is a 40-year veteran septic system installer and former designer who specializes in locating, troubleshooting and repairing systems in New Hampshire’s White Mountains. He is a past member of the Granite State Designers and Installers and maintains a troubleshooting website at


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