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RV holding tanks are a necessary part of RVing, especially when using your RV for extended periods. You may love the scenic landscapes you’ll experience in your RV, but foul smells coming from your holding tanks can ruin even the most beautiful views. So today we’re talking about the importance of fully functioning air admittance valves for keeping RV holding tank odors at bay.

What Causes RV Holding Tank Odor?

When you smell a mysterious odor in your RV, your black tank may spring to mind quickly, but it’s not always the culprit. While an RV’s gray tank doesn’t contain raw sewage, it collects bacteria-filled dishwater, food particles, body oils, and soap. When this combination sits for extended periods, it’s a recipe for odor.

RVs have plumbing systems engineered to vent odors to the outside. Air admittance valves are often a part of this engineering, so if you’re getting foul odors inside your RV it could signify a faulty valve.

Foul odor under sink can indicate a bad air admittance valve.
If you smell a foul odor and follow your nose to the area under your RV’s sink, you may have discovered a bad air admittance valve.

What Are Air Admittance Valves and How Do They Work?

Air admittance valves are critical components in plumbing systems… not only in RVs but also in standard residential plumbing. Air admittance valves allow air into the system through a one-way valve, allowing water to flow smoothly and preventing the formation of a vacuum in the plumbing system.

When water flows down a drain, it fills the space previously occupied by the air. But as the water passes through the plumbing, it needs to be able to draw air in as it goes by so that a vacuum isn’t formed. This is where air admittance valves come into play. They are one-way valves designed to allow air INTO the drain pipes, not out of them.

As water flows down the system, the air admittance valve opens, allowing air to enter through it and into the drain plumbing as the water flows into the gray tank. This ensures that the flow doesn’t create a vacuum that could siphon the water out of the p-trap (the North American term for a trap in a plumbing line). The water that stays in the p-trap is supposed to be there to block odors from escaping through your sink drain.

Without air admittance valves, a large flow of water down the drain could siphon that water out of the p-trap. If that happens, odors from the gray tank can escape through the drain in your sink.

Once the flow of water slows or stops, the air admittance valve closes, preventing any gases (a.k.a. odors) from escaping the gray tank or drain plumbing. If there’s not enough water in a P-trap, you’ll experience signs of a faulty air admittance valve – namely a nasty odor.

⬆️ ⬆️ Watch the video embedded at the top of the post for an animation showing this at 1:48! ⬆️ ⬆️

How to Know If Your Air Admittance Valve Is Faulty

Odor is frequently an indicator of a faulty air admittance valve. As odors from your RV’s gray tank escape into the living space, the noticeable smell will grow stronger, often to an unbearable level that you can’t ignore.

So, if you smell something foul, check this valve first. You’ll smell the odor throughout your RV, but it will be more powerful the closer you get to your sink.

Many RVs have air admittance valves in the cabinet under their sinks, but your RV’s construction could be different.

If the valve failed and is remaining open when it shouldn’t (after the water has finished draining), the strongest smell will be under the sink, since the valve isn’t closing to prevent odors in the gray tank from escaping into your cabinet.

If the valve failed the other way, and isn’t opening when it should (while water is running down the drain), the odor will be strongest coming out of the sink drain itself, since the air admittance valve didn’t prevent the p-trap from being siphoned. This allows the odor to get past the p-trap and come out the drain.

Either way, the air admittance valve needs to be replaced.

Air admittance valve
When our RV’s air admittance valve stopped functioning properly, we found our valve located under the galley/kitchen sink and replaced it very easily.

Even if you’re not currently experiencing this issue, it’s worth researching and noting where your air admittance valves are located for future reference. Doing so will save you time and trouble should you experience an issue in the future.

How to Replace RV Air Admittance Valves

Finding the valve is often the most challenging part of replacing it, but your nose is likely to be your greatest assistant in this process. Look underneath your sink(s)… the air admittance valve is usually installed at the top of a length of pipe that extends up, almost to sink level. They may be hard to tell apart from the drainpipes they are attached to, often looking like a cap.

Air admittance valves are incredibly easy to replace or upgrade and typically require no tools or assistance. The valves have threads on the bottom so they simply need to be unscrewed to remove them (depending on how old they are, you may need a plumber’s wrench or large pair of channel lock pliers to get it loose). Once removed, it’s easy to screw the new air admittance valve on until it’s snug, but don’t overtighten it. And that’s it!

Replacing a failed valve is a great opportunity to upgrade it to a higher-quality one, too (the ones that RV manufacturers choose aren’t usually the best… shocking, we know!). When we replaced our failed air admittance valves, we used these:

Once replaced, you can 0pen a window or two to clear the foul odor, and you’ll be back to enjoying the comforts of your RV in no time.

Other Ways to Reduce RV Holding Tank Odor

While this can be one cause of RV holding tank odors, it’s certainly not the only one. Following are a few other possible culprits and solutions to research, should you smell a foul odor inside your RV.

Upgrade The Plumbing Vents On Your Roof

Roof vents can be a source of foul odors entering the RV.
Our 360 Siphon roof vents create sufficient negative pressure in the system to keep odors out of our RV.

Your RV’s holding tanks need to be vented as well, ensuring that as water enters and fills them, the air has someplace to go (other than into the RV). So vent pipes are installed into the tops of the tanks, running directly to the roof to provide a route for the air to escape.

Standard plumbing roof vents that are installed at the factory are simple caps designed to prevent debris from entering, and blocking, the pipe. But they can actually cause problems with airflow… in the right (or wrong) conditions, they can allow wind to blow down the pipe, pressurizing the tank and pushing odors out into the RV.

Replacing those standard roof vents with something that’s better designed can eliminate that problem… and even help prevent odors by ensuring there’s a constant flow of air up and out the vent pipe. That’s why we installed 360 Siphon Vents in place of our standard plumbing vents. When the wind is blowing across the roof (in any direction), these clever vents use the venturi effect to draw air up and out through the vent pipe, helping to keep odors flowing in the right direction… away from you!

Lippert Components 389381 360 Siphon Roof Vent Cap - White (Gen 2)
  • ELIMINATES ODOR - Exhausts odors out the roof vent before they have a chance to invade your RV
  • COMPATIBILITY - Engineered for a universal fit, the 360 Siphon is compatible with all RV vent caps

Regularly Clean Your Holding Tanks

Think for a moment of all the items that go down your RV drains and into your holding tanks. In addition to the raw sewage that ends up in the black tank, the gray tank accumulates food particles, soap, body oils, and other substances.

If you have a flush valve on your holding tanks (much more common on black tanks than gray), using them regularly will help reduce these unwelcome additions from your tank. If not, you can fill your tanks with clean water to remove unwanted particles. Filling and emptying with fresh water can help rinse 0ut odor-inducing particles from your holding tanks. If you don’t have a built-in tank flush system, a wand that goes down the toilet is a great option for rinsing the black tank.

Use Holding Tank Deodorizer

There are many holding tank deodorizers on the market. These products not only speed up the process of breaking down leftover food particles and bacteria, but they can also leave a pleasant scent. Deodorizers continually release their odor-fighting chemicals as the pod contents break down in the tank.

Use Holding Tank Enzymes to Help Break Down Waste

They’re not just for your black tank! For maximum efficiency in all of your RV waste holding tanks, you can use specially-designed enzymes to break down waste. These products are specifically engineered to target large and small chunks of waste and food. Enzymes attack these waste particles and break them down, so they’ll flush out the next time you empty your RV’s holding tanks.

We’ve been happy with a product called Happy Campers, an organic holding tank treatment.

HAPPY CAMPERS RV Holding Tank Treatment - 64 Treatments
  • ODOR FREE: Eliminates odors in the RV holding tank. Absolutely no chemical or sewer smell.
  • Septic tank friendly

If you’re in a situation where stubborn odors just won’t go away, or you’re having the common problem of tank sensors that read incorrectly, or not at all, there’s an additional step available — Power washing your holding tanks! We recently shared our experience of having our black and gray tanks blasted for the very first time.


It’s easy to take for granted a fresh-smelling RV until foul odors invade your living space. Conducting regular preventative maintenance and using a combination of cleaning methods is the best way to keep your RV holding tanks clean and odor-free.

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Sometimes we receive products for evaluation at no cost and may use affiliate links to the products and services from which we earn commissions. For example, as an Amazon Associate, we earn from qualifying purchases. That said, it's important to us to let you know that our opinions are our own. We only recommend products we believe deliver real value and that we can confidently recommend without reservation. You also won’t pay an extra penny by using our links. Thanks so much for supporting RVgeeks as we work to create helpful RVing-related content that we hope enhances your RVing life!

Even though we're handy RVers, we're not professional technicians. So although we're happy with the techniques and products we use, you should be sure to confirm that all methods and materials are compatible with your equipment and abilities. Regardless of what we recommend, consult a professional if you're unsure about working on your RV. Any task you perform or product you purchase based on any information we provide is strictly at your own risk.

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