RV Holding Tank Odor Control ? – Air Admittance Valves

TheRVgeeks Plumbing, Repair 32 Comments

We haven’t had RV holding tank odor problems in years, but after a recent two-week boondocking stay, we had a BAD gray water smell. Check out the video to see what the problem was, and how easy it was to fix it. We installed 360 Siphon vents on our roof years ago, and haven’t had any problem with tank odors since…. at least that was true until the right conditions combined to cause a nasty smell.

If you’re not familiar with air admittance valves, this short video might just make your RV much improved in the olfactory department. ?


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Comments 32

    1. Post
      Author

      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.

  1. 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

    1. Post
      Author

      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.

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

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      Author
  3. 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.

    1. Post
      Author

      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.

  4. 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

    1. Post
      Author

      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.

      1. 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

        1. Post
          Author

          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!

  5. Well very well explained and the visuals were great as usual. Thanks will check ours when we get back. You two rock

    1. Post
      Author

      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. ?

  6. 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.

    1. Post
      Author

      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!

  7. 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.

    1. Post
      Author

      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! ?

  8. 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?

    1. Post
      Author

      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. ?

  9. 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.

    1. Post
      Author

      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!

  10. 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.

    1. Post
      Author

      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!

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      Author

      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!

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