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RV Holding Tank Odor Control and the Importance of Air Admittance Valves

RV Holding Tank Odor Control and the Importance of Air Admittance Valves

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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TBoneCO

Thursday 21st of April 2022

I know this is an old post, but is it normal for a gray water pipe to dump into the black tank? I noticed on my RV that the bath sink drain is plumbed directly into the black tank vent pipe. Only thing protecting the interior from the black tank smell is the p trap and AAV (aka studor vent, anti-syphon vent) and the black tank vent.

TheRVgeeks

Thursday 21st of April 2022

There are indeed some RVs that have the setup you're describing, often due the plumbing and/or tank location and configuration. It's good that you're aware of it, since smelling black water (vs gray water) will be the alert that you may be having an issue with your AAV or other component. Might be a good reason to replace your roof plumbing vent with a 360 Siphon, at least if you're having odor issues. How to Replace an RV Plumbing Vent (and Upgrade It!)

Pat Parker

Friday 4th of June 2021

Do these air admittance valves screw on all types because i noted that you can chose an abs or pvc adapter. Do i need two one for the bathroom and one for the kitchen as I think it would be a good idea to change them out because as with your RV ours is 15 years also

TheRVgeeks

Monday 7th of June 2021

BTW... most RV drain plumbing is ABS (black) because it's stiffer, sturdier, and better able to handle sudden temperature changes (plus it only requires a single-step process for gluing the pieces together, which makes it easier for the manufacturers). PVC tends to be white and is a little more pliable.

TheRVgeeks

Friday 4th of June 2021

When we get a chance, we’ll check out your air admittance valves, and let you know how they look. ????

Steve

Monday 13th of May 2019

Does the shower have an air admittance valve? Great video.

TheRVgeeks

Monday 13th of May 2019

Hi Steve! Good question. Ours doesn’t, because it’s tapped into the vent line to the roof, so it doesn’t need one. But there’s no standard for how this is done... and another viewer commented that their shower had an AAV mounted on plumbing inside the wall! So your mileage may vary, depending on your manufacturer, floor plan, etc.

Terry E Underwood

Sunday 12th of May 2019

Thank you for getting back to me about the odor in my rv. Going to order the 360 tomorrow. I have a 2016 entegra aspire question I have for you is about the Tecma toilet like to see you do a video about that type have you ever used one I can only go 4 DAYS before dumping black tank because it Use lots of water to flush please get back to me

Terry Underwood

TheRVgeeks

Sunday 12th of May 2019

We’ve never used a Tecma toilet, and obviously don’t have one to do a video about, but we do know a bit about them. In general, macerating toilets, especially those in rear baths that are far from the black tank, do use more water to pump waste forward to reach the tank. That said, they do have a low water setting that saves somewhat on water. Personally we are fans of regular toilets placed directly over the black tank, but that is not always an option, depending on floorplan. Any of us who are really serious about conserving water, have the option of considering a composting toilet, which uses none at all. We don’t have one, but we have several friends who do, and they like them a lot.

Roger B

Sunday 12th of May 2019

Wow! That's great information. I had no clue about the engineering of the grey water system. Thanks for that info.

TheRVgeeks

Sunday 12th of May 2019

Thanks Roger! Always great to hear we’ve been helpful. ?

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