RV Holding Tank Sensors: How They Work and How to Clean Them

August 31, 2021

RV Holding Tank Sensors: How They Work and How to Clean Them. Unique Camping + Marine

Key Points:

  • Tank sensors function like a circuit; the rising water level completes the circuit and lights up the level gauge
  • Sensors typically misread because they are covered by something (human waste, TP, grease, oils, etc.)
  • Cleaning your sensors in both tanks can be done easily, even overnight while you sleep; full-time RVers will need to modify the black sensor cleaning process so they can continue using the tanks while cleaning
  • Popular techniques and cleaning products in the RVing community are sometimes not all they are cracked up to be; do your homework before using them
  • Adopt The Unique Method to avoid sensor issues in the future

If you’re struggling with misreading holding tank sensors, you’ve officially joined the ranks of the RVing community because this is one of the most common problems. And this article will provide you with all the guidance you need to understand why sensors misread and how to restore them easily and without damaging your wastewater system. Without properly functioning sensors, it’s hard to know when your wastewater tanks are full so you can dump them. It’s a frustrating problem that even experienced RVers deal with. Unfortunately, many seasoned campers have concluded that sensors will always fail, so you can’t rely on them; they just ignore their sensor readings because they know their routine well and dump their tanks according to routine usage. But the good news is that in most cases, misreading sensors can be restored by maintaining thorough and proper cleaning habits and using the most effective sensor cleaning products.

In this article we will walk you through everything you need to know about your sensors:

  • How your sensors work and why they are misreading
  • The difference between black and gray tank sensor problems
  • Steps you can take to clean and restore your sensors
  • An overview of available cleaning products and methods and our opinions on their performance
  • Best practices that will help ensure your sensors keep working properly

Let’s be clear about one thing up front: the best way to avoid malfunctioning sensors altogether is to follow The Unique Method. But reality is that even when it seems like you're doing everything right, sensors can still misread. For the majority of RV owners, misreading sensors is a very fixable problem, so don’t feel bad if you’ve been struggling. 

How do RV tank sensors work?

In most cases, an RV tank sensor is mounted on the inside of your tank but some models are mounted on the exterior. Sensors are typically situated in four places vertically on your tank wall:

  1. Top
  2. One third down from the top
  3. Two thirds down from the top
  4. Bottom

When the level of water in your tank reaches each sensor, they act as conductors, completing a circuit and lighting up that level reading on the sensor monitor box. 

What Causes RV Holding Tank Sensors To Misread?

The quality of RV wastewater tank sensors are typically very poor, so it’s easy to get false readings if you’re not properly treating both your gray and black tanks. Sensors can misread for two reasons:

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

Like we explained above, sensors are just circuits that are waiting to be completed by the water level. This means that anything that is covering the sensor (even if it’s not water) can cause the circuit to report tank contents have reached that level when in reality they have not. This problem is fixed by cleaning the debris off the sensors. This cleaning process varies between black tanks and gray tanks, but if you've applied our recommended cleaning techniques a few times and your sensors still don't read correctly, there is a good chance they are broken and need to be replaced.

Tip: If you routinely struggle with keeping your sensor probes in good operating condition, you might consider installing exterior-mounted sensors, like SeeLevel RV Tank Sensors. Aftermarket sensors like this are a great option if you want more reliable readings on tank levels because it won’t be possible for waste and grease to stick to the sensors and cause misreads. However, if a piece of waste becomes stuck to the inside wall right where the sensor is, it could still misread, so be sure you are practicing good tank care habits even if you use exterior sensors (refer to The Unique Method for more information).

Reasons for Black Tank Sensor Misreadings

The accumulation of solid waste and toilet paper are the main causes of misreading RV black tank sensors. Liquefied and sometimes even solid poop can cake onto your sensors when consistent tank cleaning habits are absent. In the same way, toilet paper can get caught on the sensors, especially if you use a lot or if you don't use a high-quality, bacteria-based, solid-reducing holding tank treatment like Unique RV Digest-It. If you use the proper care techniques (as we describe in The Unique Method), it’s much less likely you will encounter misreading black tank sensors.

Reasons for Gray/Galley Tank Sensor Misreadings

You might be wondering what could possibly coat your gray/galley holding tank sensors. There’s nothing solid like poop or paper in your gray or galley tank, right? Not usually, but there is more than solid human waste that can accumulate on sensors. Food waste, grease, oil, and fats cause most of the gray water sensor issues during normal use; and it’s not just food grease. Common, everyday items like soap and shampoo can also contribute to residue buildup on your tank walls, coating sensors in a thick slime. Most of the time, this type of residue buildup is seen when dry camping/boondocking where the gray tank valve must be closed and greasy water is able to sit idle and cling to the holding tank sensors as the water level rises. It's usually not as much of an issue for campers on hook-ups, but regular deep cleanings and consistent, healthy care habits (as we describe in The Unique Method) will help you avoid sensor issues no matter what kind of camping you do.

How to Clean Your RV Holding Tank Sensors

Now that we’ve covered the reasons for sensor malfunction, you need actual action steps to perform a sensor cleaning like a champ. Because we believe so strongly that our sensor cleaning product is the best, we use Unique Sensor Cleaner as the example product in our instructional steps for cleaning and restoring black tank sensors. We use Dawn Ultra as the example product for cleaning and restoring gray/galley tank sensors because it is the best grease-eating dish soap on the market and will not disturb the beneficial bacteria colonies that may be in your tank.

Step-by-Step Instructions: Cleaning Black Tank Sensors

Step-by-Step Instructions: Cleaning Gray Tank Sensors

Which Products or Methods are Most Effective for Cleaning RV Sensors?

The best way to keep sensors clean is always following The Unique Method, which is a 50/50 approach: 50 percent in the type of products you use and 50 percent in the care habits you practice. But there is always the possibility that you will be dealing with misreading, dirty sensors and need a fix now. There are lots of product options when it comes to cleaning sensors, but you should know the benefits and drawbacks of each before making a decision. Some of the categories of RV tank sensor cleaners and methods are:

  • Bacteria and enzyme blends
  • Surfactants (soaps) and The Geo Method
  • Dawn Ultra dish soap
  • Ice and Driving Technique
  • Drain openers and chemical cleaners (not recommended)

We cover each of these product types and cleaning techniques in depth in our Choosing the Right Products or Methods for Cleaning RV Sensors guide.

Best Practices for Preventing Sensor Problems

Sensor issues can often seem overwhelming, and they may not be fixed overnight, but there are certain steps you can take to prevent them in the future. From our conversations with thousands of RVers, we’ve developed a comprehensive, proven wastewater treatment process called The Unique Method. Below, we have provided a high level checklist of The Unique Method's practices that will help curb sensor problems in the future, but we highly recommend reading through the entire guide on The Unique Method to get the more extensive information:

  • Use your tank valves correctly (black is always closed; gray is open when on hook-ups and closed when dry camping/boondocking).
  • Treat your holding tanks with a high-quality bacteria and enzyme product (preferably not chemical cleaners).
  • Fill your toilet bowl with water before you use it.
  • Keep water in your toilet bowl (unless driving).
  • Hold down your toilet flush pedal for at least 10 seconds every time you use it.
  • Dump your tanks every 3-5 days.
  • Flush your tanks very well every 3-5 dumps.
  • Prevent as much grease and food debris as possible from getting in your gray/galley tanks.
  • Don't clean your toilet, sinks, dishes or showers with chemical or antibacterial cleaners.
  • Deep clean your black tank twice per year and your gray tank after each dry camping/boondocking trip.
  • Store your RV with a full black tank of water and a bacteria and enzyme solution if there is no concern of freezing.

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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