I recently helped out a homeowner in Pittsburgh. His wife had decided it was time to tear out an outdated platform bathtub. She wanted to replace it with a new, sleek soaking tub shaped like an elongated vessel sink. I must admit, these tubs look amazing and they’re also very comfortable.

However, after removing the tub and its platform, it became apparent to my reader that the plumber who installed the platform tub took a shortcut and installed the required vent pipe for the tub drain line on top of the bathroom’s subfloor. There was sufficient space to do this beneath the platform, and the installation met code requirements.

However, the homeowner wasn’t sure what he could do to relocate the drain line. Fortunately, he supplied me with photos which made it easy to troubleshoot his problem. I described how he could relocate the vent pipe so it was no longer above the floor and yet would meet code and function properly.

His dilemma is a reminder that more homeowners need to understand the importance of plumbing vent pipes. These pipes provide the pathway air must follow when you flush a toilet, use a washing machine or brush your teeth.

Before you turn on a faucet, the only water in your home’s plumbing pipes is dormant in a P-trap located beneath a fixture or floor drain. This water provides a barrier that prevents vermin and sewer gas from entering your home. When no water is flowing, both the drain pipes and the vent pipes are simply filled with either air or a mixture of air and sewer gas.

The minute you flush a toilet or run water from a fixture, you introduce water into the drain pipes. This water displaces the air and pushes it down the drain pipes in the same way that a snowplow pushes snow. The air must be replaced immediately — and this happens via air drawn down through one or more pipes protruding from your roof.


If enough water travels fast enough through plumbing drains and the vent pipes are clogged or missing, a vacuum will form and the needed air will enter the system via one of the plumbing P-traps. You may have heard a slurping noise from a tub or sink when you flushed a nearby toilet or a washing machine started to pump water into the system. These noises are the sounds of air entering the system. This is not a good thing, as the P-traps then lose their ability to fend off sewer gas and vermin. To maintain proper venting, there must always be an open pathway up from each fixture to the roof.

So how can you assure that your vent pipes are sound? I prefer venting plumbing fixtures with pipes which interconnect with one another and eventually exit through the roof.

You can have multiple vent pipes poking up through the roof to save on pipe material. It’s also easy to flash vent pipes so you never have a roof leak. I prefer to use a flashing boot made by Lifetime Tool that has a powder-coated metal base and a special silicon-rubber boot that’s superior to plain rubber boot flashings used by most plumbers.

Every few years, assuming you can climb onto your roof safely, you should put a garden hose down the roof vent pipe and run water down the pipe for a few minutes to wash out accumulated dust, tree debris or even bird poop.

If you do this, assign sentries within the house to spot any leaks. Although rare, it’s possible a vent pipe in an attic or wall might have a crack or an improperly sealed fitting. This might not be a problem for air, but it becomes a big issue when gallons of water travel through the vent pipes.

Station someone by the hose spigot who can turn off water immediately if a leak appears. You’ll benefit from discovering this leak, as it could be the reason you notice a sewer gas smell every now and then.

Tim Carter has worked as a home improvement professional for more than 30 years. To submit a question or to learn more, visit AsktheBuilder.com.