Gray Tank & Sensor Cleaning

TheRVgeeks Plumbing, Quick Tips 20 Comments

Besides water, an RV gray tank (or “grey” if you trend more British) takes in lots of greasy, sticky substances. These include food particles & residue from preparing meals and washing dishes, soap, shampoo, toothpaste & even body oils. After a while, it can gum up your holding tank sensors, causing a false reading on your tank monitors.

Cleaning out the gray tank and sensors is a really simple task, since there’s a readily available liquid designed to break up all of the crud that can build up in the tank: automatic dishwasher detergent. The gel type is easy to flush down the drain, and goes right to work breaking down and dislodging greasy build-up.

To calibrate the holding tank monitors in your RV, follow the steps outlined in our video:

Calibrate RV Tank Monitors

To clean your gray tank, simply choose a day when you’re about to take a long road trip to a full hook-up RV park. Just start with about a half-full gray tank, pour about one cup of automatic dishwashing detergent gel (NOT standard dishwashing soap like Dawn or Palmolive… you DON’T want something that’s going to suds up!) into one of the sinks, and wash it down the drain with plenty of hot water. Then spend a few hours on the road, allowing the sloshing action in the tank to work with the detergent to break up any nasty gunk that’s accumulated. The longer and twistier the road the better, but a few hours of agitation should be plenty.

Once you arrive at your full hook-up campground (a dump station will of course work fine as well), simply pull the gray valve and dump the tank. All of the greasy gunk that was stuck to the tank will get flushed out with the water.

If your “3/4” or “full” light is the one staying on, start your trip with a fuller tank, which will ensure good water agitation on that sensor. But since the heaviest buildup is generally in the lower part of the tank, 1/2 tank or so should provide a good combination of water and empty space for strong agitation and sloshing as you drive.

If the first try doesn’t clear up the problem, just try it again on your next long road trip. It’s so easy and inexpensive that another attempt is no big deal. Once your tank is clean, your sensors should work fine and any odors you may have been experiencing should be eliminated or reduced as well (yes, gray tanks can smell too).

We're handy RVers, not professional technicians. We're happy with the techniques and products we use, but be sure to confirm that all methods and materials you use 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.

We sometimes receive products for evaluation at no cost, and The RVgeeks are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to and affiliated sites. But our opinions are our own, you won’t pay an extra penny, and we only link to products we personally use, love and can recommend to friends with complete confidence.

Comments 20

    1. Post
  1. Hello!
    I have a 14 year old toter home (neglected gray tank for the past 12 years… not our doing) and it seems if the gray does not get dumped within 2 days it wreaks… almost bird killing smelly… I can’t get to the tank from uptop to clean it and it has no flush, any chemical treatments I can use besides this one?

    1. Post

      Oh boy, Bryttany. We feel for you on this one. Inheriting someone else’s gray/black tank problems can be a nose full! ? We haven’t ever had to deal with that directly ourselves (we’re the only owners of our RV), but one thing we’d suggest that you try is using a product like Happy Campers Extreme Clean (you can get it here on Amazon: It’s an extra-powerful biological & enzymatic tank treatment that might be able to help break down the “stuff” in your tank that is causing the nasty odors. You might have to treat the tank a couple of times to get it all removed (if you can fill the gray tank with a treatment or two and let it soak for a couple of days, that might really help). Then, once it’s clean, using the regular Happy Campers Tank Treatment (yup, also available on Amazon: in your gray & black tanks should help keep the odors at bay.

      Another possibility, if the Happy Campers isnt’ able to clear up the smell, is that you could have a blocked vent pipe on your gray tank. Typically, your tanks have one or more pipes that connect from the tank up through the walls of the RV to the roof, so that as the tank fills, air can be pushed up them (so the tanks don’t get pressurized). This helps manage odors, too… routing them up onto the roof and away from your nose. If they are blocked (a buildup from stuff in the tank at the bottom end, or a wasp/spider’s nest somewhere along the length of the vent pipe), the air can’t escape and it may be finding another way out.

      Lastly… it’s possible that you have a failed/failing Air Admittance Valve (AAV) under one of your sinks. If you can isolate where the odor is strongest when it happens, you may be able to find it. The AAV is a small cap that is installed on a vertical section of pipe you’ll see tee’d off your plumbing lines under your sinks. They’re designed to be one-way valves, allowing air into the plumbing to prevent a large flow of water (like when you drain a full sink) from siphoning all of the water out of the P-trap under the sink. If that AAV fails, it can either allow the P-Trap to be drained (which allows odors from the gray tank to come right up out of your sink drain) OR van allow odors out from the valve inside the AAV itself (which allows odors from the gray tank to come right up UNDER your sink… so if you open a sink cabinet and the smell gets worse, that’s your likely culprit). The AAVs are easy to replace… they usually just screw right off the top of that vertical pipe… and a new one screws right back on. Easy-peasy.

      Hope one of these ideas helps you solve the odor problem!!

  2. My RV has been stationary for about 10 years my gray tank is full of solids how do I clean that because it’s beginning to plug up,and we don’t drive it, not even sure if it drives anymore?

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      Hi Gary! You mentioned that it’s your gray tank, but we just want to confirm that you don’t mean your BLACK (toilet) tank, since those are the ones that are more prone to solids building up. We’d suggest closing the valve and filling the tank with water and an extra heavy dose of Happy Campers Extreme Clean and let it soak for a couple of days. If it’s really bad, it may take more than one treatment. You can find Happy Campers Extreme here on Amazon:

    2. Say “good bye” to those crappy tank sensors that foul up all the time and say “hello” to SeeLevel RV tank sensors. I converted my Itasca a few months ago and what a difference! I know exactly how much I have in each tank, including the propane, to within a gallon or so. This is HUGE if you do a lot of boondocking. No more guessing. Easy to install if you can get at your tanks. Readout is in percentage of full at the push of a button, one for each tank. It also includes a digital readout voltmeter which is way better than those LED, guess how much charge I have left, indicator lights. Like night and day.

      1. Post

        LOL! Thanks for that input, Joe. We’ve definitely had our eye on the SeeLevel system for some time now. We really want to install one, but have been a bit lazy about doing it because the sensors Newmar uses are external to the tank and don’t get crudded up… so we’ve adapted to knowing how much capacity we have left when the black/gray tank monitor reads 3/4 full. But knowing an exact percentage, instead, would be SOOOOO nice! May just have to move that project up on the list! ?

  3. I tried this when I had 2 lights that would stay on. I tried the dish washing liquid and now I have 4 lights on. What can I do now to clear these lights or what is the issue? I have 2 gray water tanks and 1 black water tank. I treated all the tanks and now all the tanks have 4 lights on.

    1. Post

      Hi Carter! Sorry for the delay in responding… your comment got caught as Spam and we just found it. It sounds like one of several issues:

      • You’ve got something coating the sensors in all three tanks (which would seem like an unlikely coincidence, but it’s possible that something in the tanks/water reacted with the dish washing liquid and left a film)
      • You’ve got an electrical issue (are your batteries fully charged? Tank sensors rely on voltage/current measurements between the sensors… so low/high voltage could be causing an error)
      • Your display panel has failed in some way

      Going with the simplest-solution-is-usually-the-right-one approach, we’re guessing it’s that something’s coating the sensors. You said you tried “dish washing liquid” in all the tanks, since it happened after you treated the tanks (and because the other two issues are less likely). Did you use the soap you use to hand-wash dishes at the sink (like Dawn or Palmolive)? Or what we recommend – dishwasher detergent that you put into a dishwashing machine? The former (dish soap for hand washing) will cause a problem because it will suds up too much… and the suds could actually be making the sensors think that the tank is full of water when it isn’t… it’s just full of suds! You want dishwasher detergent because it doesn’t suds up very much… and the suds that DO form break down very quickly. DishWASHER detergent is mostly a heavy-duty softener… so it allows the water to penetrate and remove “gunk” that’s crudded up.

      You may need to flush your tanks with fresh water a couple of times to get rid of the soap residue and/or suds… then try soaking them with the non-sudsing dishwasher detergent. If that doesn’t work… you could try soaking them with something like Happy Camper Extreme Clean (available on Amazon: ) to try and break up whatever’s clogging your sensors.

      THEN… if all of that doesn’t work, it may be time to check for electrical/electronic malfunctions.

      Hope this helps… and let us know how you make out!

  4. In addition to your excellent video on how to empty your black tank, would you recommend this same cleaning process for the black tank and its sensors as part of annual maintenance or some other frequency?

    1. Post

      Hi John,

      This isn’t something that we do on any kind of a schedule. It’s only an “as-needed” type of treatment. A tank that’s well-cared for on a regular basis shouldn’t have this come up very often, if at all.

  5. Just wanted to say Thank You for this video. We’ve been dealing with a stuck sensor for several weeks and all the usual suggestions failed. We drove about 5 hours yesterday with a half full tank and some Cascade and Voila! Clean sensor!!! Your site is incredibly helpful! Thanks so much!

    1. Post

      Thanks for letting us know! It’s always nice to hear that our videos are actually helping people. We’re happy that your sensors are working again… it’s never nice not knowing your tank levels! Safe travels!

  6. Have you guys ever looked into the SeeLevel products that give the exact percentage of used (or unused) portion of your tanks? The sensors are on the outside of the tanks and never build up gunk, etc. I like you have a Newmar with the exact same readout y’all have and have been mostly satisfied with the results. However, something about knowing the exact percentage of fluids versus the big gaps of only 4 readouts is intriguing. Also note I am in NO WAY affiliated with the product but was curious if y’all also have looked into it like I have.

    1. Post

      We sure have looked at SeeLevel, and would really like to upgrade, but somehow have never gotten around to it. We’re hoping to make time to complete our research, try it out, and of course make a video about it at some point.

    1. We’d recommend following the same soaking process, but of course without the driving/agitating part. Also, you might consider keeping your gray valve closed sometimes. That way when you empty it, the rush of water will help remove food particles and other debris and help keep things from building up in the first place. During the times you’re using the tank with the gray valve closed, adding a cup of water softener should also help keep things from sticking in the tank. Hope this helps.

        1. Post

          Any automatic dishwasher detergent should do the job for gray tank cleaning, since it doesn’t suds up. We don’t recommend regular dish soap (Dawn, etc) for tanking cleaning for just that reason…. suds!

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