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.
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.
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
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!
- Prevents odors and gases from invading RV living space
- Speeds up waste breakdown, eliminating the need for chemicals
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.
- ODOR FREE: Eliminates odors in the RV holding tank. Absolutely no chemical or sewer smell.
- Biodegradable, environmentally friendly, 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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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
When we get a chance, we’ll check out your air admittance valves, and let you know how they look. 😁
Okay great because we could smell some gray smell and it went away when I closed the grey valve to the sewer connection…just saying. Thanks again Pat
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.
Does the shower have an air admittance valve? Great video.
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.
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
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.
Wow! That’s great information. I had no clue about the engineering of the grey water system. Thanks for that info.
Thanks Roger! Always great to hear we’ve been helpful. ?
Have you investigated the Hepvo waste valve. It is suppose to eliminate the air valve and give more room under the sink by eliminating the P trap. Any thought on using one of these in your coach.
We’re familiar with Hepvo valves, but simply made the decision not to install them, because they aren’t perfect either. The low water flow from extensive boondocking can really gum things up in the drain, requiring removal and cleaning of the stopper, and if installed, a Hepvo valve. That’s not necessary with traditional P traps. We’re all in on going with more complex / more expensive solutions when they provide a high level of betterment. We’re not convinced that Hepvo valves fit the bill. That said, they are really useful for places where space is limited.
ok great video have one question for you we are full timer and stay for a mo at a time so I leave my grey tank open all the time and still get that odor under my bathroom sink I have change both of the one way values what more can I do
thank again
terry underwood
bhttoy@gmail.com
Hi Terry. We leave our gray valve open all the time as well. We would first suggest that you try closing the gray valve, to see if the odor is coming up out of the RV park sewer system. Also, have you tried installing 360 vents on the roof? And one other thing you could try is creating a P-trap in the sewer hose right before it enters the RV. If you look for our video “Gray valve open or closed?” we address how to do that. Hope this helps.
I have another question about the 360RV vents. In your video the top of the cap shows its upward. When I go to Amazon and I look at those The indentation of the cap is inwards so therefore it would collect water. Were did you get the one on your video please look and you will see what I am talking about
Terry
Hi Terry. Ours is one of the original design units. Since we bought ours, the design has changed to what you’re seeing on Amazon. From what we understand about the new design, it works exactly the same as the style we have. As far as collecting water, we wouldn’t worry about it. There are likely many dips/low spots in your roof itself that collect as much, if not more, water when it rains, etc. We bet it dries up just as quickly once the rain stops. ?
Hope this helps!
Well very well explained and the visuals were great as usual. Thanks will check ours when we get back. You two rock
Thanks ladies! If you’re not getting any gray tank odor in your RV, your admittance valves are probably fine. We’ll be happy to check for you next time you come out. ?
Great job as usual! That’s the valve I put on mine last year to replace the cheapie factory original that stuck even when new. Had to cut down a coupler to adapt the new one to fit the factory vent pipe, but worth the extra effort.
Thanks, Greg! We’ve had one or two similar situations where RV plumbing wasn’t quite standard, so buying a typical household replacement required some form of adapting or MacGuyvering (is that a word?!?!) to get it in place. Glad you got yours taken care of… and hope you haven’t had any more odor issues since!
Thank you guys! You taught me something…. yet again. I had this problem in my last motorhome’s bathroom sink for a while and didn’t know the science, mechanic or parts involved. So, I started tossing chemicals down the drain to mask the smell. Being it my first RV I figured I was at fault somehow or it is just one of those temporary things that is part of the RV lifestyle. I don’t know that my admittance valve was ‘bad’, since the problem did go away eventually and the RV was only 3 years old. But now I know about this part, the role it plays and that there is a better widget out there to experiment with.
Glad this was informative, walkerhound! Tracking down odor issues in an RV can be quite the game of cat and mouse, since the problem can come and go, and it’s hard to isolate the combination of conditions/events that cause them. Sometimes it’s odors from the tank roof vents getting blown into an open vent fan or other path into the RV. Sometimes it’s an air admittance valve that’s failed. Sometimes it’s a P-trap that dried out or got suctioned dry (due to a failing or insufficient air admittance valve). And on and on. There are a lot of factors at play. But at least now you’re armed with some more information if it ever happens to you again! ?
We had a smell when we started out on a trip as well. I thought it was the black tank roof vent letting odors in via a fan I forgot to close. But all the fans WERE closed and the odor went away after a few minutes. Now I know what to look for next time it happens and will pick up a few of the AAVs for when it does.
By the way, did your odor issue start as an intermittent, lesser smell problem? Or did the big stink happen all at once?
Hi John. Our odor problem happened all at once… VERY suddenly. For some reason, odors get sucked up and swirl around the passenger seat (lucky me!), so it was VERY apparent, VERY quickly that we had a problem. And it was made worse by opening the driver’s side window (which creates negative pressure in the RV and drew MORE odor in through the AAV!!!).
We have had intermittent odors in the past, and always assumed it was something similar (strange combination of wind direction blowing odors coming out of the roof tank vents toward somewhere that let it come into the RV), but could never isolate them. So it’s possible that it was the AAV failing over time, letting little bits of “perfume” into the interior.
It’s also possible that if an AAV fails in the opposite way and won’t OPEN, that you could have an issue with the P-trap under a sink getting suctioned out when you dump tanks before leaving a site. Then the odor comes up through the sink drain… and if there’s JUST enough water in the trap that it lets air out occasionally while sloshing back and forth while driving. So you get hints of odor while on the road, but then when you slow/stop… they go away. And once you run water into that sink, the trap fills back up and problem’s solved again until next time. ?
Excellent video. We had our air admittance valve fail under our bathroom sink. It not only resulted (initially) in the bad smell. it somehow allowed water to flow from our black tank clean out hose into the RV and discharged under the sink instead of into the black tank. I replaced it with the same Studor valve you chose, nearly 18 months ago and the problem ended.
Hey Charles. It actually sounds like what failed was the vacuum breaker on your tank flush system. It looks similar to an AAV, and is usually installed inside a cabinet under a sink. It’s supposed to ensure that water from the black tank can’t back-flow out the connection to city water used for flushing. If you look under that sink, you’ll likely see that there are two air-admittance-valve-looking devices there. (although there’s no standard, so your RV could be plumbed differently than ours and others we’ve seen).
Regardless… so sorry to hear that you had it fail in such a way. Hope you caught it quickly and didn’t end up with too much of a flood! And glad you’ve got it all fixed up!
Thanks for the link to the improved valve! Great post, as always. Our grey tank air admittance valve is giving us issues also. Problem is, its buried in the wall between the shower and the refrigerator, tucked behind a pocket door. I saw it back when I rebuilt the shower, but it wasn’t an issue then. For now, we will just have to keep the grey tank drained.
Oh, man! Talk about lack of planning on the manufacturer’s part! Putting an air admittance valve where it can’t easily be reached is a major problem!
Thank you, the information was good!
Thanks, Larry! Glad you enjoyed it!
Always great videos!!!! Gray water does not hurt mother earth!!!! Water a catcus!!!
Thanks, Scott! LOL! Good advice… but be aware of the rules/regulations regarding gray water where you are to be sure you’re not violating them!
Great explanation!
Thanks, Stephen!
Great video. I always wondered what that did.
Thanks, Larry! Glad to solve that little mystery for you! ?