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Ask the Builder: Solving Sewer Gas Mysteries

BY Tim Carter TIMEJuly 18, 2022 PRINT

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

I’ve been a master plumber since 1981, and I always say if you have a daughter, son or grandchild who wants to have a rewarding career that provides significant income, point them to a trade school that teaches this craft.

Today I want to talk about sewer gas. It’s vital that plumbing drain pipes, as well as the vents that connect to them, be installed correctly so sewer gas never enters your home. Every week, I solve sewer gas problems over the phone with homeowners. In fact, on the day before I wrote this column I solved a vexing problem for a New Mexico homeowner just hours before he was expecting house guests.

Sewer gas can be found in septic tanks, city sewers and the drain pipes in your home. It smells horrible. It’s caused by the decomposition of bodily waste and rotting food that you send down your drain pipes. It’s toxic and can cause severe illness if you’re exposed to enough of it for long periods of time.

Just two years ago a man hired me to come to his home to solve a sewer gas issue. His wife was ill and no doctor could figure out the cause. Within minutes, I connected her suffering to the leaking sewer gas. I found out that they had installed a new tile floor on top of an existing one in a powder room adjacent to where his wife sat and watched TV.

After the new floor had been installed, the tile setter or plumber failed to install an extra wax ring to account for the fact that the toilet now sat a half-inch higher than it had 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, the sewer gas stopped entering the home.

It’s vital to understand that the plumbing pipes in your home work like the blood vessels in your body. When all is well in your body, your blood stays inside the blood vessels. If you cut yourself or if a vessel breaks under pressure, blood leaks out. The same is true for the pipes in your home. When all is well, the liquids, solids and sewer gas stay in the pipes.

But if a pipe cracks or has a hole drilled in it, or if a trap under a fixture dries out, you’ll have trouble. Dried-out 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 a U shape, that traps water at the bottom of the curve, and this acts as a barrier to gas and vermin entering your home.

p-trap
This is a p-trap, although it’s not a common design. As long as it’s filled with water, this device stops sewer gas and vermin from entering your home. (Tim Carter/TNS)

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

Many of the condo owners only stay in their units for a few months out of a year, and while they’re gone, water evaporates from the traps under all the fixtures and from the toilet bowls. Once the water seal in the traps is broken, the sewer gas wafts into the unit and then enters the tall plumbing shaft where all the pipes go down to the street. The sewer gas in the tall shaft was getting into the man’s condo.

I had him contact the condo maintenance manager. He used his master key and went into each vacant condo. He then ran water in all the fixtures and flushed all the toilets. Within hours, the sewer gas problem in the entire building stopped.

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

A year ago I wrote a simple booklet about 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 narrow down the potential sources. Within a few minutes, you will likely be able to figure out the problem on your own. If not, I am available to talk on the phone.

If you want to read the first chapters of my short sewer gas book for free, go here: https://GO.askthebuilder.com/sewergasbook

Subscribe to Tim’s FREE newsletter at AsktheBuilder.com. Tim now does livestreaming video M-F at 4 PM Eastern Time at youtube.com/askthebuilder.

©2022 Tim Carter. Distributed by Tribune Content Agency, LLC.

Tim Carter
Subscribe to Tim's FREE newsletter at AsktheBuilder.com. Tim now does livestreaming video M-F at 4 PM Eastern Time at youtube.com/askthebuilder. (C)2022 Tim Carter. Distributed by Tribune Content Agency, LLC.
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