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RV Blank Tank Shows Full When Empty? Dirty Sensors

One of the first things many people learn when they start RVing is that RV tank sensors are notoriously inaccurate. We have had 5 RVs, and all of them have shown full black tanks when they were actually empty. Unfortunately, no matter what you do, these sensors are nearly impossible to depend on fully.

Today, we’ll help you learn why your black tank shows full constantly, and we’ll even share some tips for cleaning an RV tank sensor. Let’s get started!

Close up of RV panel with RV black tank sensor
RV black tank sensors can help you determine when it is time to empty your black tank.

Why Does My Black Tank Show Full When Empty?

Your black tank shows full when empty because the tank sensors are dirty. They’re detecting the presence of solids or liquids and reporting it to you. Unfortunately, when this occurs, something sticks to one of the sensors inside your black tank and causes an inaccurate reading of your tank levels.

To fully understand why this happens, let’s examine how black tank sensors work.

RV dump tank station
When emptying your tank, toilet paper and other solids may get stuck on your sensor causing it to read that it is full when it isn’t.

How Does an RV Tank Level Sensor Work?

RV tank sensors sit inside the tank wall and typically connect to lights in a control panel that RVers can check. As the tank fills with solids and liquids, it reaches the sensors at various heights. A simple circuit measures the level of the tank and turns a light on if it’s within a certain specification. It’s a simple design, but it’s not fool-proof.

Because freshwater tanks only contain water, nothing can stick to the sensors inside the tank. These sensors are typically incredibly accurate and can help you know how much available fresh water you have.

Jayco RV black tank sensor panel
Cleaning your RV tank sensor will ensure it doesn’t always read that your tanks are full.

How Do You Clean and Reset a Black Tank Sensor?

Solid materials can easily stick to the sides of your black and gray tanks and their sensors. They may even dry to the sensor if you leave them for long enough. If you want your sensors to work, you need to keep them as clean as possible.

Fortunately, the step-by-step process to clean your black tank sensors is simple and straighforward.

How to Prevent Your Black Tank Sensor From Malfunctioning

There are a handful of things you can do to prevent your black tank sensors from having inaccurate readings. Here are some valuable tips for always getting accurate readings from your tank sensors.

1. Use Proper RV Black Tank Cleaners Regularly

A dirty tank sensor is the most common reason your sensor shows the black tank is full when empty. If you want to avoid these issues, keep them clean with proper RV toilet chemicals. Camco’s TST Max pods and the Happy Camper powder formula are some of the most popular tank treatments. 

Camco TST MAX Camper / RV Toilet Treatment...
  • POWERFUL RV BLACK TANK TREATMENT: Eliminate clogs & odors in your...
RV Black Water Tank and Sensor Cleaning

2. Don’t Leave Your Black Tank Open

Leaving the black tank open when hooked up to a sewer connection drains out all the liquids, but not the solids. The solids can build up at the bottom, offsetting the ideal liquid-to-solid ratio to properly breakdown the solids.

The unofficial term in the RV community for this is a “poop pyramid.” This occurs because the solids, toilet paper, and poop pile into a pyramid at the bottom of a black tank. If you leave it for an extended time, this pyramid can harden and cause a blockage in your RV’s plumbing system. You may even be unable to dump your tanks.

Pro Tip: These tips on how to Simplify Black Tank Dumping with an RV Macerator Pump will change your RVing game!

Close up of hoses to empty black tanks
Always ensure that there is a generous amount of water inside of your black tank to help your sensor from malfunctioning.

3. Regularly Flush Out the Black Tank

Many modern RVs come with black tank flush connections making it easy to flush out the black tank.

  • If you use your RV for recreational trips on the weekend, you’ll want to flush out your tanks after every trip.
  • If you’re traveling full-time in your RV, flush out your system every third or fourth time you dump your tanks.
  • If your RV doesn’t have a black tank flush, you should still flush out your system. In these situations, flushing the toilet is the easiest way to fill up your black tank.

4. Add Water Into Your Empty Black Tank Before Use

Another common mistake many RVers make is insufficient water in their black tank. After dumping your black tank, you should always fill your toilet with water and flush it at least once. Water helps break down the solids and avoid anything sticking inside your tank.

How To Empty Black Tank & Grey Tank In An RV - Camper- RV Newbie 🤓

Keeping Your Black Tank Maintained Is a Relief

Unfortunately, there’s not much you can do about the unreliability of black tank sensors. There are other solutions for black tank sensors, but they’re substantially more expensive. If you experience an inaccurate black tank level reading, don’t panic. If you dumped your tanks recently, there’s a good chance they’re empty, and something is sticking to the side of your black tank.

Use plenty of water when flushing, and keep several gallons in your black tank to prevent potential issues. If you do, you’ll reduce the number of inaccurate readings and know what to do when you experience them.

How often does your RV tank sensor give an inaccurate reading? Tell us in the comments!

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About Tom Morton

Tom, a Pacific Northwest native, is our technical genius. Born in Washington and raised in Alaska before settling in Michigan. He's the man who keeps our operation running, both figuratively and literally.

With a background in Electrical Engineering, Tom specializes in RV solar systems and lithium batteries. He made history as the first documented individual to use a Tesla battery module as an RV battery. Tom has personally assisted countless RVers with system installations and has educated thousands more through his videos and articles.

Cinematography is another of Tom's passions, showcased in his work on the Go North series. You can see his camera skills on display in The RVers TV show on Discovery Channel and PBS where he also stars as a co-host.

Tom's mechanical expertise extends beyond RVs to boats, planes, and all things mechanical. He's renowned for taking on maintenance and repair projects single-handedly and is often spotted underneath RVs, making him the technical backbone of our endeavors.

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Saturday 6th of January 2024

We no longer put TP down the toilet, instead we use an empty disinfectant canister lined with a vegi bag from the grocers. It has a lid and is discarded every day. No muss, no fuss, no stink, no stuck and the sensor is always right on

The Mortons

Sunday 7th of January 2024

Great solution Suvane for no fuss and more accurate black tank sensors!