How to Clean and Restore RV Holding Tank Sensors

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Article 3 of 5 in Series: RV Holding Tank Sensors

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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. 
  • Cleaning black tank sensors is an easy process using Unique Sensor Cleaner; repeating the process may be necessary to remove stubborn waste from the sensors.
  • Cleaning gray tank sensors is an easy process using grease-eating Dawn Ultra dish soap.
  • Cleaning sensors in your combo tank depends on how you’re using it; you may need to try both the black and gray sensor cleaning processes.
  • When sensors still misread after multiple cleanings, they may just be broken and need replacement.

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 gray tank sensors. We will also touch on the process to clean black/gray combo tank sensors.


Why Are Your Tank Sensors Malfunctioning?

Let’s quickly review why your sensors may be misreading. 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

Steps for Cleaning 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 (make sure you dump at an approved dumpsite).
  7. Flush your tank very thoroughly with a built-in rinser, rinser wand, or backflusher (if you’re not sure how to use one of these tools, refer to our guide on How to Use RV Tank Rinsers and Other Rinsing Tools).
  8. Close your black tank valve.
  9. Test the sensors by filling the black water tank again to make sure the level gauge shows tank levels correctly.
    • If the sensors read correctly, dump the tank. You’re done!
    • If the sensors are still misreading after a second or third cleaning with Sensor Cleaner, there could be two courses of action:
      1. You can try using Draino, but we recommend trying again with Sensor Cleaner before using Draino. Caustic chemicals included in products like Draino could cause damage to seals, valves, and other components of your tank, so be cautious if you choose to use it.
      2. Your sensors may be broken and should be replaced; contact our customer service team if you need assistance with finding the best course of action to fix the problem.

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).

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.


Steps for Cleaning 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 accumulate 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 and won’t harm any beneficial bacteria you might be adding with tank treatments. 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.

Before starting this process, if you are a hook-up camper who leaves the gray valve open, be sure to close your gray water valve.

  1. Before you go to bed, fill your tank with water (as high as the highest misreading sensor).
  2. 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.

  3. Let this sit in the gray water tank and pipes overnight while you sleep.
  4. In the morning, open your gray tank valve and dump the tank (make sure you dump at an approved dumpsite).


    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.

  5. Repeat this process the next night (if necessary) until sensors are restored to proper functionality.
    • If the sensors read correctly, dump the tank. You’re done!
    • If the sensors are still misreading after a second or third cleaning with Sensor Cleaner, there could be two courses of action:
      1. You can try using Draino, but we recommend trying again with Dawn Ultra before using Draino. Caustic chemicals included in products like Draino could cause damage to seals, valves, and other components of your tank, so be cautious if you choose to use it.
      2. Your sensors may be broken and should be replaced; contact our customer service team if you need assistance with finding the best course of action to fix the problem.

The process is the same for all types of campers, so clean your gray tank sensors as often as you feel necessary.

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.


Cleaning 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 combo tank sensors restored to proper functionality, 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, like these SeeLevel RV Tank 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 Black Tank Sensor Cleaning for Full-Time RVers

If you are a full-time RVer, cleaning RV black tank 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 in order to continue using them should still help to a point.

The gray tank process is the same for full-time RVers as it is for everyone else, so refer to the Steps for Cleaning Your Gray Tank Sensors. Just remember, Sensor Cleaner and Dawn Ultra can only clean sensors they can reach; sensors not touched by water will not be cleaned.


Review

Let’s briefly review what we covered in this article:

  • Sensors misread because something other than water is covering it, fooling them into reporting that tank contents have reached that level. 
  • Clean black tank sensors using Unique Sensor Cleaner; full-time RVers will need to modify this process to accommodate continued tank use.
  • Clean gray tank sensors using grease-eating Dawn Ultra dish soap overnight while you sleep.
  • You may need to try both black and gray sensor cleaning processes when cleaning combo tank sensors; it all depends on how you’re using it.
  • 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.

We talked a lot in this guide about using Unique Sensor Cleaner for black tank sensors and Dawn Ultra dish soap for gray tank sensors, but you may have seen people in the RVing community recommending other sensor cleaning products and techniques. We want you to have all the straight information on the techniques and products available so you can make your own decision about what is best for your RV. The next article will cover some of the most popular cleaning methods and products and our opinions on their effectiveness.

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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!

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