Stink Bombed

by Bob Livingston | Jul 19, 2024 | Pro Tip, RVEXPERT

a man leans close in to an RV bathroom sink while pinching his nose

When the air becomes tainted with noxious odors from the gray-water holding tank(s), the culprit is usually a bad air admittance valve. Replacing this valve with a Studor Mini-Vent will keep your nose happy.

Sanitation systems in any RV are great to have — heck, they are a necessity — but keep in mind that you will likely be hauling around the “stinky stuff” that resides in the holding tanks. Handling the contents always brings sneers from outsiders, but taking care of the sanitation system is not really that bad.

Well, until the stink arrives.

Recently, at the end of one leg of a long trip in hot weather, I opened the entry door to my fifth wheel and was hit with very recognizable “stinkum” — and knew right away that the air admittance valve (AAV) in the bathroom and/or kitchen sink had seen better days.

Now, most people don’t know — or believe — that gray water can stink worse than black water for a number of reasons, including the fact the most people don’t flush these tanks while dumping; RVs are just not set up that way. Fortunately, the AAV is designed to control sewer gases that end up wafting through the P-trap — and it’s very simple to replace.

The AAV is mounted on the end of a pipe that extends from the P-trap above the point where the gray water enters the pipe that is routed to the holding tank. When water is flowing through the P-trap, the AAV opens to allow air to flow into the pipe and closes when the flow stops. If the valve does not close fully, then an obnoxious odor is allowed to permeate the area around the sink and makes its way throughout the interior. And to your nose.

The solution is very simple: Remove the old AAV and screw on a new one.

But hold on; not all AAVs are created equal. While the ones provided by the RV manufacturers will work, they seem to fail much more often than those found in stationary homes. And they always fail at inopportune times.

A great replacement AAV is the Mini-Vent from Studor, which is a household product name among the home-building trades. They are readily available at hardware and home-improvement stores and usually sell for around $15. The Studor Mini-Vent has a much more robust seal and is designed to flow more water. And, they usually last for a long time — sometimes as many as 15-20 years in stationary homes.

The Mini-Valve is commonly sold with an adapter to make it fit 2-inch pipes, which is not necessary since RVs use 1 ½-inch pipes. The ones we bought at Lowe’s have a PVC adapter, but you can get an ABS adapter, if for some reason your RV has 2-inch pipe.

a hand removes the adapter for 2-inch pipe from the Studor Mini-Vent main piece

When the air in the fifth wheel started to stink, a leaking air admittance valve (AAV) was pinpointed as the culprit. While factory AAVs seem to work for a while, a better choice was to replace it with a Studor Mini-Vent. This product comes with an adapter for 2-inch pipe but is not necessary in RVs so it can be discarded.

Studor Mini-Vent placed beside the the stock AAV showing the black stock AAV is taller than the white Studor Mini-Vent

top view of both the Studor Mini-Vent and the stock AAV showing the Studor Mini-Vent is slightly wider than the stock AAV

The Studor Mini-Vent is not as tall as the stock AAV, but it’s wider, which may create a clearance problem in some RVs — particularly under the bathroom sink.

Installation should be as easy as unscrewing the original AAV and installing the new one. The only caveat is clearance: In some cases (mostly under a bathroom sink), the pipe is routed to accommodate the stock AAV, which has a smaller diameter than the Mini-Vent or other similar products on the market. This was the situation for our installation. Fortunately, there was enough “play” in the pipe configuration to make the Mini-Vent work with just a touch of bending. If the pipe is too close to the side of sink bowl, then pipe rerouting will be necessary, as was the case when a neighbor installed a new AAV.

view upward from the base of the bathroom sink piping at the tight clearance of the installed Studor Mini-Vent

As you can see, clearance is tight in this installation under the bathroom sink. The AAV is usually installed on the top of the pipe above the junction of the P-trap and pipe that leads to the holding tank. Fortunately, there was enough play in the pipe to install the larger Mini-Vent AAV.

close view of the seal in the original AAV

The seal in the original AAV had seen better days and became somewhat brittle. When the seal leaks, the tainted gases can permeate the interior of the RV.

The old AAV should come off without a lot of twisting pressure and there will usually be some pipe sealant to clean up. Once the old AAV is off, the threads in the pipe can be wiped with a paper towel before applying Teflon tape to the threads on the new part. You should only need one wrap of Teflon tape, but make sure it’s good stuff. One of my favorite brands of Teflon tape is Blue Monster PTFE Thread Tape, which sells for $16.74 on Amazon (three rolls of ½-inch wide by 1,429 inches long).

one wrap of quality Teflon tape is added to the Studor Mini-Vent to seal the treads

The worst part of removing the old AAV and installing the new one is getting your hands under the sink(s), especially if you are not limber. The AAV simply screws on to the end of the pipe. After cleaning the old sealant off the pipe threads (not shown) we added one wrap of quality Teflon tape to seal the AAV threads (not shown) we added one wrap of quality Teflon tape to seal the treads. The AAV does not need to be super-tight.

under the sink view in the RV galley at the stock AAV with plenty of clearance

under the sink view in the RV galley at the new Studor Mini-Vent with plenty of clearance

As you can see, there was plenty of room inside the island-counter sink in the galley. Although the old AAV was smaller, there was no issue with clearance here when installing the new Mini-Vent. Once the new AAVs were installed, the odor was gone.

Once the new Mini-Vents were in place, the odor was immediately eliminated — and my sense of smell got much-needed relief.

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