How to Clean and Restore RV Holding Tank Sensors

August 12, 2021

How to clean and restore RV holding tank sensors. Unique Camping + Marine Guides and Resources

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Key Points:

  • Black water tank sensors misread because poop and toilet paper are caked on the sensors and gray sensors misread because they become layered with grease and oils, causing them to read “full” when the holding tank is only partially filled. 
  • Restoring black tank sensors is an easy process using Unique Sensor Cleaner; repeating the process may be necessary to remove stubborn waste from the sensors
  • Restoring gray tank sensors is an easy process using grease-eating Dawn Ultra dish soap.
  • When sensors still misread after multiple cleanings, they may just be broken and need replacement.
  • The best way to prevent misreading sensors in the future is to follow The Unique Method.

For those who have dealt with misreading sensors, you know how frustrating that can be, especially when you’re in the middle of a boondocking trip and you still have several days to go! Is your tank full or not? It’s a very important question to be able to answer and unfortunately, sometimes your sensors fib. But don’t take them to the woodshed! The process for cleaning misreading sensors in both black tanks and gray tanks is fairly simple. Keep in mind that the process is a little different between the two types of tanks because each requires a different product to get the best results. In this article, we’ll show you how to use Unique Sensor Cleaner to clean RV black tank sensors and Dawn Ultra dish soap to clean and restore your gray tank sensors. We will also touch on the process to clean black/gray combo tank sensors.


Why Are Your Tank Sensors Malfunctioning?

Sensors malfunction for only two reasons:

  1. Something is covering the sensor
  2. Sensors are broken

Different things can cover the sensors depending on the type of tank.

  • Black water tank sensors– human waste or toilet paper
  • Gray/galley tank sensors– grease and oil
  • Black/gray combo tank sensors– human waste, TP, grease and oils can all contribute

If you want more information on how the sensors work and the pros and cons of popular cleaning techniques/products, refer to the Cleaning RV Holding Tank Sensors guide.


Restoring Your Black Tank Sensors

Cleaning RV tank sensors and restoring them to their best is quite easy using Unique Sensor Cleaner; it can be a little more challenging for full-timers who need to use the black water tank while cleaning the sensors, but we have that process covered too!

  1. Close your black tank valve.

  2. Fill your tank with water (as high as the highest misreading sensor).

  3. Shake your bottle of Sensor Cleaner very well.

  4. Pour half the bottle into your black water tank through the toilet.

  5. Let sit for as long as possible (we recommend 72 hours or more if possible).

    Note: There is no amount of time that is too long to let Sensor Cleaner work; the longer the better! Sensor Cleaner can be left inside a black water tank for weeks or months at a time without doing any damage.

  6. Open your black tank valve and dump your tank.

  7. Flush your tank very thoroughly with a rinser wand or back flusher.

  8. Feel free to test the sensors by filling the black water tank again to make sure the level gauge shows tank levels correctly.

  9. Close your black tank valve.

    • If the sensors read correctly, dump the tank. You’re done!

    • If the sensors are still misreading, repeat this process once more to be sure Sensor Cleaner has had enough time and contact with the sensors to clean them well. If they still misread after a second or third cleaning, they may just be broken and you will have to replace them.

The process is easy if your RV is sitting in your driveway not being used, but it gets much more challenging when full-time RVers are trying to clean black tank sensors and use the tank at the same time (refer to the Modified Sensor Cleaning for Full Time RVers section below). If you’ve followed this process and your sensors still don’t work, there could be two reasons:

  • There is so much waste caked on the sensors that you may need to apply one more treatment with Unique Sensor Cleaner or you can try using Draino, but we recommend trying again with Sensor Cleaner before using Draino.

    Note: Caustic chemicals included in products like Draino could cause damage to seal, valves, and other components of your tank, so be cautious if you choose to use it. This is why we recommend trying another treatment of Unique Sensor Cleaner and our customer support team is available to help you apply additional treatments.

  • Your sensors may just be broken and should be replaced, but we recommend trying a second or even third treatment of Unique Sensor Cleaner before assuming the sensors are broken.

    Note: Refer to the guide on Full Time RVing: The Definitive Guide To Treating Your Tanks for more details on the best ways to treat your tanks while full-time RVing.


Restoring Your Gray Tank Sensors

Unlike black tanks, gray water tank sensors are actually pretty painless and inexpensive to restore. Even full-time RVers will have an easier time cleaning their gray tank sensors than they would cleaning black tank sensors. Sensors loaded with human waste and toilet paper require a strong bacteria and enzyme cleaner like Unique Sensor Cleaner , but gray water tank sensors contain mostly grease and soap residue. The best way to remove this layer of grime is to use a strong grease-digesting dish soap. We always recommend Dawn Ultra Dish Soap because it's a fantastic grease-eater and pretty inexpensive; we even recommend using it to clean your dishes because it will continue cutting grease inside the tank(s) after the dishwater is drained. We normally recommend buying Dawn Ultra in a large container since you may need to repeat this process several times to fully clean the sensors.

  1. Before you go to bed or on your last night boondocking, close your gray tank valve (hook-up campers).

  2. Fill your tank with water (as high as the highest misreading sensor).

  3. Pour 20 ounces or more of Dawn Ultra down your RV’s kitchen sink line (if you think you’ve added enough, add a little more; the more you add, the tougher it will be on grease).

    Note: You may start to see it foaming back out of your sink or shower lines. That’s okay; it means it’s spreading its grease-zapping power throughout the pipes as well and tells you exactly when you’ve added enough.

  4. Let this sit in the gray water tank and pipes overnight while you sleep.

  5. In the morning, open your gray tank valve and dump the tank.

    Note: There's a very good chance you'll see a grayish/white residue on the bottom of your holding tank discharge pipe. This is the grease that was previously clinging to the inside walls of your holding tank.

  6. Repeat this process the next night (if necessary) until sensors are restored to proper functionality.

It may take several applications to completely restore the sensors, and in most cases, one or more applications of Dawn Ultra will do the trick. However, sensors could still misread after the first application of Dawn Ultra, in which case there are two possible reasons for the continued misreading sensors:

  • There is so much grease and oil caked on the sensors that you may need to apply one more treatment with Dawn Ultra dish soap. Some people may decide to try using caustic chemical products like Draino to clean gray tank sensors, but we recommend trying again with Dawn Ultra before using Draino.

    Note: Caustic chemicals included in products like Draino could cause damage to seal, valves, and other components of your tank, so be cautious if you choose to use it. This is why we recommend trying another treatment of Dawn Ultra and our customer support team is available to help you apply additional treatments.

  • Your sensors may just be broken and should be replaced, but we recommend trying a second or even third treatment of Dawn Ultra before assuming the sensors are broken.

    Note: Refer to the guide on Full Time RVing: The Definitive Guide To Treating Your Tanks for more details on the best ways to treat your tanks while full-time RVing.


Restoring Sensors in Your Black/Gray Combo Tank

Cleaning and restoring sensors in your black/gray combo tank may look a little different depending on how you’re using it.

If you’ve tried these techniques, including the cleaning steps for both black and gray tanks and have still not seen your sensors restored to proper functionality, just like two sections above, we recommend trying multiple treatments before using a caustic chemical product like Draino or assuming your sensors are simply broken. You can also install external level sensors that will not easily be blocked by debris because they are on the outside of the tank; however, debris sticking to the inside of the wall right in front of the external sensor can still cause a misread, so be sure you are following The Unique Method’s guidelines to keep tanks clean and free of waste residue.


Modified Sensor Cleaning for Full Time RVers

If you are a full-time RVer, cleaning RV tank sensors can be a lot trickier when you’re trying to use the wastewater holding tanks at the same time; you may not have the ability to fill the tank completely with water (which is ideal). If you suspect a sensor issue and need to clean them while using your tanks, fill your black tank(s) half or three quarters full with water (depending on anticipated usage), add one bottle of Unique Sensor Cleaner per black tank, and continue regularly using your toilet, ideally letting the solution work for a full 72 hours before dumping.

The best option is always to clean sensors without using the tanks so that the cleaning solution can reach even the highest sensor, but modifying the cleaning process while still using them should help on some level regardless. The gray tank process is similar but with a few differences. Just replace the sensor cleaner with 20 oz. or more of Dawn Ultra dish soap in each of your gray/galley tanks and let it sit overnight while you sleep. Dump the next day. Just remember, Sensor Cleaner and Dawn Ultra can only clean sensors they can reach; sensors not touched by water will not be cleaned. 

Consistently practicing The Unique Method will also help prevent the majority of RV tank sensor problems before they happen, so we recommend following this method regularly. For more thorough details on full-time RVing care habits, refer to Full Time RVing: The Definitive Guide To Treating Your Tank


Preventing Sensor Issues

Because misreading sensors can cause serious anxiety in the middle of a trip, we recommend adopting The Unique Method to prevent sensor misreadings in the future. The Unique Method is a proven process for caring for wastewater holding tanks. It is a 50/50 approach: 50 percent the right care habits and 50 percent the right products. Using this method is always the best way to avoid malfunctioning sensors, but here are a few related guides and quick tips for maintaining functional sensors that are pulled right from The Unique Method:


Preventing Black Tank Sensor Misreadings
  • Use a high-quality, waste-digesting tank treatment to help liquefy the waste

  • Always flush/rinse your tank after dumping

  • Deep clean your tank at the start and end of the season (dry campers/boondockers) or every 3-5 dumps (full-time RVers)

  • Don’t use too much toilet paper

  • Use lots of water

  • If your RV will be stored for even a short amount of time, consider storing it with a full black tank of water and an entire bottle of Unique Sensor Cleaner (when there is no danger of freezing)

Guide: Why You Should Use a High-Quality Waste Digester in Your RV

Guide: You Need to Perform an RV Holding Tank Flush

Guide: Deep Cleaning RV Wastewater Holding Tanks

Guide: Why is Adding Water to Your RV Black Tank Important?


Preventing Gray Tank Sensor Misreadings
  • If you’re on hook-ups, keep your gray tank valve open

  • Wipe your dishes of food particles and grease as much as possible

  • Use a sink strainer to catch errant food particles from going down the drain

  • Use Dawn Ultra dish soap to wash your dishes (maybe even pour a little down the sink to get ahead of the grease)

  • Deep clean your tank at the start and end of the season (dry campers/boondockers) or every 3-5 dumps (full-time RVers)

Guide: The Definitive Guide to Using Your RV Waste Water Valves

Guide: Deep Cleaning RV Wastewater Holding Tanks




Adopt The Unique Method

You bought your RV so you could enjoy life and spend time with family and friends. The last thing you want to do is waste precious time and money on fixing wastewater holding tank problems. Keeping your tanks in peak operating condition doesn’t have to be hard, confusing, or expensive if you follow our proven process: The Unique Method.

The Unique Method is a comprehensive tank care plan that we developed after years of conversations with real customers facing real problems. The Unique Method provides you with simple, preventative steps to stop odors, clogs, and sensor problems before they start so you can spend less time worrying about your holding tanks and more time enjoying the freedom and adventure of RVing. Try it yourself and see why thousands of campers trust their RVs with The Unique Method every day.

If you need more help with anything covered in this guide or simply have a comment, we’re here to help you anytime!

Contact Us




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