Gray Tank & Sensor Cleaning

TheRVgeeks Plumbing, Quick Tips 14 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.

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Comments 14

  1. 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?

    1. Post

      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! 😉

  2. 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!

  3. 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.

  4. 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!

  5. 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.

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