Galley Stink Bomb

by Bill Gehr | Jul 6, 2022 | Pro Tip, RVEXPERT

When the check vent connected to the P-trap under the sink fails, plan on holding your nose. Replacement is easy, and the use of a Studor Redi-Vent will keep noxious odors at bay for a longer period of time.

When a friend called to tell me that, while boondocking at a nearby beach campground, he had a sewage smell under his galley sink and even after a thorough cleaning and tossing of unwanted supplies the obnoxious smell was still there, I knew immediately that he had a problem with the check vent under the sink.

Also called the vent valve or admittance valve, this often-ignored component is designed to vent the gray holding tank when it is physically impossible to run a vent pipe up through the roof. This is a common problem in bathroom sinks; most RVers mistakenly think this smell in the bathroom is coming from the black tank. It’s hard to believe that shower water and soapy water from doing dishes can smell this bad — but if you think about it, bacteria or even mold can develop in only a few days and, after a while, the smell can really fester as the mix of contents that are dumped into the gray tank remain stagnant. And, as my friend discovered, it’s a malady more noticeable when boondocking.

Fortunately, check vent valves are very easy to change once you know what to look for. These vents commonly have a 1½-inch tread below a dome, which serves as the check valve and can be easily removed by hand since they are not tightened to a specific torque. If they’re a bit stubborn, use a cloth to provide additional grip; in a worst-case scenario, grab a pair of off-set pliers (commonly used for plumbing repairs) to carefully break it loose.

The original check vent, mounted to a pipe next to the P-trap, had failed — and noxious odors were filling the compartment below the sink.

Standard-type check vents are simple in design, using a neoprene disc seal that moves in response to positive and negative pressure in the gray tank, created by water flow. The seal shown here has seen better days; it’s warped and will not seal, which allows odors to escape.

While common replacement valves are readily available at RV stores, a better choice is to upgrade to a 1½-inch Studor Redi-Vent (which comes with an adapter to accommodate 2-inch plumbing). This product is a one-way valve that automatically opens and takes in fresh air when it senses negative pressure from water flowing into the plumbing system. When the flow of water stops, the vent closes, essentially blocking noxious odors from escaping into the compartment and sink. The Redi-Vent is available on Amazon for $32 and can also usually be ordered at RV supply stores.

The basic-model check vents installed in most RVs have a neoprene disc-type seal, which warps over a period of time, allowing the smell from the gray tank to escape into the galley or the bathroom area. Some of the replacement check vents may be wider than the stock part, so make sure that you have enough room; for this installation, the original check vent was almost touching the galley sink, so a larger check vent could not be used. The check vent here was in a difficult spot to reach, but fortunately it was not tight, making it easy to spin off by hand.

Be sure to use Teflon tape when reinstalling the vent so that odors cannot escape around the threads, and it only needs to be hand tight since there is no pressure involved that could dislodge the part.

Higher-quality check vents, like the Studor Redi-Vent, come with an adaptor to fit a 2-inch ABS system.

wrapping the thread with good quality Teflon tape

Always wrap the threads with a good quality Teflon tape, which will prevent odors from seeping past the threads.

the check vent installed directly to the pipe

Once the Teflon tape is wrapped around the threads, the check vent can be screwed onto the adapter when working with a 2-inch system or installed directly to the 1½-inch pipe in this project trailer. Most RVs these days have a 1½-inch system.

Space was tight for installing the new check vent, but it only needs to be hand tight. Limited clearance next to the sink precluded the use of a larger check vent. Once the project was done, the owners could let go of their noses.

There also are specific gray-tank chemicals that will alleviate most tank odors and keep the monitor sensors clean. If you start using these chemicals from the beginning it will mitigate some of the particles sticking to the tank permanently and, of course, help the vent do its job of preventing odors, which can spoil the RV experience.

Needless to say, my friend’s wife was very happy when the odor was gone.

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