Ask the Builder: Solving the Mysteries of Sewer Gas | Home and outdoor

I’ve always liked doing plumbing work because it’s a real three-dimensional puzzle.

I’ve been a master plumber since 1981, and I always say that if you have a daughter, son, or grandchild who wants to have a rewarding career that pays big bucks, steer them to a trade school that teaches that trade.

Today I want to talk about sewer gas. It is essential that the plumbing waste pipes, as well as the vents that connect to them, are installed correctly so that sewer gases never enter your home. Every week, I resolve sewer gas issues on the phone with homeowners. In fact, the day before this article was written, I solved a tricky problem for a homeowner in New Mexico just hours before he was expecting guests.

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Sewer gas is found in septic tanks, municipal sewers, and the drains in your home. It smells awful. It is caused by the decomposition of bodily waste and rotting food that you send down your drains. It is toxic and can cause serious illness if you are exposed to it in sufficient amounts for long periods of time.

Just two years ago, a gentleman hired me to come to his home to fix a sewer gas problem. His wife was ill and no doctor could determine the cause. Within minutes, I connected her suffering to the sewer gas leak. I found out they had installed new tile over an existing floor in a powder room adjacent to where his wife sat and watched TV.

After the new floor was installed, the tiler or plumber did not install an additional wax ring to account for the fact that the toilet was now half an inch higher than before. Sewer gas was leaking from the base of the toilet. As soon as two wax rings were installed on top of each other on the toilet flange and the toilet was reset, sewer gas stopped coming into the house.

It is essential to understand that the plumbing pipes in your home work like the blood vessels in your body. When everything is going well in your body, your blood stays inside the blood vessels. If you cut yourself or a vessel ruptures under pressure, blood will flow out. The same goes for the pipes in your home. When all is well, liquids, solids, and sewer gases remain in the pipes.

But if a pipe cracks or has a hole in it, or if a trap under an appliance dries up, you’ll be in trouble. Dry P-traps under sinks, showers and floor drains are the most common source of sewer gas. The p-trap incorporates a curved pipe, most often U-shaped, which traps water at the bottom of the curve, and this acts as a barrier to gas and vermin entering your home.

Two years ago, I did a phone consultation with a man who owned a condo in a high-rise building in Monaco. He had a horrible sewer gas problem. It turned out that gas was leaking from several other units above and below his apartment!

Many condo owners only stay in their unit for a few months a year, and while they’re gone, water evaporates from the traps under all the fixtures and from the toilet bowls. Once the seal on the traps is broken, sewer gas enters the unit and then enters the large plumbing pit where all the pipes go down to the street. Sewer gas in the large well was entering the man’s apartment.

I asked him to contact the condo maintenance manager. He used his master key and entered each vacant condo. He then ran water through all the fixtures and flushed all the toilets. Within hours, the sewer gas problem throughout the building stopped.

Wind can also cause a problem. That plumbing pipe on your roof runs the opposite of chimneys. Chimneys are designed to get rid of smoke from a fire or furnace. Plumbing vent pipes draw fresh air into your home’s pipes every time you run water in a sink or shower or flush the toilet.

A year ago I wrote a simple pamphlet on sewer gas. It explains how plumbing systems work. If you have a sewer gas problem, the book asks you a series of questions to help you narrow down potential sources. Within minutes, you’ll probably be able to fix the problem on your own. Otherwise, I am available to speak on the phone.

If you want to read the first chapters of my little book on sewer gas for free, go here: