One of the first things many RVers learn when they start RVing is that RV tank sensors are notoriously inaccurate. We have had 5 RV’s and all of them have had this problem. Unfortunately, no matter how much money you spend on your rig or time cleaning your RV tank sensor, sensors are nearly impossible to depend on fully. Many find that their black tank shows full when it’s empty, making it challenging to manage their tank levels. If you’ve ever experienced this problem with an RV tank sensor, you’re not alone. Luckily, there’s something you can do about it!
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!
What Is an RV Black Tank?
An advantage of an RV is that it allows you to travel to exciting places and have access to a kitchen, a comfortable bed, and a bathroom. Since many of these exciting locations won’t always have a bathroom, an RV uses a few storage tanks for freshwater, black water, and gray water. While fresh water is pretty straightforward as the water is safe for drinking, it’s easy to confuse the black and gray tank.
Black tanks on an RV contain any solids or liquids you flush down an RV’s toilet. The tank becomes a mixture of water, sewage, and toilet paper. Depending on the size of your tanks and how many people use the restroom in your RV, you can typically go for a week or more without needing to empty this tank. However, it’s crucial to empty it at the end of every trip, especially if your RV will sit in storage.
On the other hand, the gray tanks on an RV contain anything that goes down a sink or shower drain. While most of these tanks will be soapy water, they’ll also have food particles and oils from food and your skin. Many people fear the smell of their black tank, but don’t underestimate how stinky a gray tank can be.
While each tank has a unique job, they all work together to allow RVers to enjoy their RV. Learning to manage your tank levels is a necessary skill you must develop, especially if you plan to go boondocking, dry camping, or camping in a location without a sewer connection on-site.
Pro Tip: Use our RV Black Water Tank Survival Guide to learn all you need to know about your tanks before you hit the road!
Why Does My Black Tank Show Full When Empty?
It’s not uncommon for a black tank RV sensor to show that it’s full when empty. Many RVers experience this frustrating situation during their adventures. New RVers may even consider hitching up their rig and hauling it to a repair shop to have them fix the issue. However, despite paying big bucks to have a shop fix the sensors, the problem will likely appear after another time or two of using their RV.
Your black tank shows full when empty because the tank sensors are doing their job. They’re detecting the presence of solids or liquids and reporting it to you. Unfortunately, when this occurs, something has stuck to one of the sensors inside your black tank and is causing the inaccurate reading of your tank levels.
To fully understand why this happens, let’s examine how black tanks work.
How Do Black Tanks Work on an RV?
Black tanks store the solids or liquids that flush down a toilet in an RV. When an RVer empties their black tank into a sewer connection, the waste inside the tank quickly dissipates. However, toilet paper and other solids can remain stuck inside to the walls of the tank.
Most RV tank sensors sit inside the black tank along the sides of the tank to measure the depth of the contents inside. If any solid materials stick onto one of the black tank sensors, it will cause an inaccurate reading. The only way to remove the material from the black tank sensor is to flush and clean your tanks thoroughly.
There are some sensors that are more accurate than others particularly the sea level sensors or sonar-based ones. These types of sensors do not need anything protruding into the tank that can get gummed up.
How Often Do RV Black Tanks Need to Be Emptied?
How often you empty your RV black tanks depends on how large your tanks are and how many people are using the restroom in your RV. Some RVers with large tanks and only a few people using the bathroom can go one to two weeks before dumping their tanks. On the other hand, larger families in smaller RVs may fill their black tank during a weekend camping adventure.
If you plan to spend time in rustic campgrounds or boondocking situations, making your black tank last as long as possible is essential. So is cleaning your RV tank sensor. You want to avoid packing up your campsite or cutting your trip short because you need to dump your tanks.
How Do You Know When Your Black Tank Is Full?
While your freshwater tank sensors tend to be incredibly accurate, the sensors on your black tank can be inaccurate. As a result, it’s nearly impossible to trust them. Luckily, you can usually tell when your black tank is full when your black tank sensors are letting you down.
First, it’s crucial to know that you’ll eventually get a feel for how long you can make your tanks last. If you get into a routine of using your RV, you’ll likely know that you must dump your tanks every X amount of days. However, since RVing can be exciting, it can also be easy to forget the last time you dumped your tanks.
Knowing when your black tank is full without using your sensors is easy. The waste that you flush into the toilet will start to fill up the black tank. Every flush will push solid and liquid materials into your black tank and replace the air that’s sitting in your tank. As the tank gets full, this escaping air will create a gurgling or bubbling effect in the toilet. Once you notice this occurring, it’s a sign you need to start planning when you’ll dump your tank next because it’s reaching capacity.
With many RV toilets its also possible to look down the toilet and actually see the fluid and solid levels. You can do this by opening the toilet valve and looking down inside with a flashlight. It may be gross, but can be a good way to see the level.
RV’s with macerating toilets cannot use these methods, however, but luckily most of these have additional sensors for the toilet itself that are more accurate. If a macerating toilet does not stop flushing its very messy because it is pumping the waste in with a motor.
How Does an RV Tank Level Sensor Work?
There are a few different RV tank sensor types but the most common is the resistive measurement design. The sensors sit inside the tank wall and typically connect to lights in a control panel that RVers can check. As the tank fills up with solids and liquids, it reaches the sensors at various heights. A simple circuit measures the resistance of the sensor circuit and turns a light on if it’s within a certain specification. It’s a simple design, but it’s not always practical.
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 fresh water you have available.
Black and gray tank-level sensors can be hit or miss regarding their accuracy. Solid materials can easily stick to the sides of your tank and the sensor. 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.
How Do You Clear and Reset a Black Tank Sensor?
To clear and reset a black tank sensor, you need to clean it. The most effective way of cleaning your RV black tank sensor is to empty and flush your black tank. Next, you’ll want to put several gallons of water into your black tank. You can use a black tank flush connection or flush your toilet several times.
The next step in cleaning your tank sensor is to take your RV for a drive around the block or to your next campsite. You’ll dump your tanks again after the drive. The clean water sloshing inside your black tank should do the job. If not, you can beef up your efforts by dumping a bag of ice into your black tank in addition to the several gallons of water. The ice can provide help to knock off any solid materials stuck to the inside of your RV black tank and assist in cleaning the sensor.
Its also possible to have your tanks professionally power washed. We hung out with our friends the RV geeks while they had their tanks washed out. You can watch the video below.
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.
Clean the Sensor If Your Black Tank Shows Full When Empty
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. There are various waste tank treatments you can purchase to help your black tank break down its contents. This helps ensure solids leave your tank as efficiently as possible when emptying your tank.
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Don’t Leave Your Black Tank Open
One of the biggest mistakes an RVer can make is to leave the black tank open when hooked up. Just because you’re connecting your RV to a sewer connection does not mean you can leave your black tank dump valve open the entire time. To properly flush a black tank, you need a combination of solids and liquids.
The force of gravity pushing the liquids out of the tank also carries the solids out. If there aren’t enough liquids, the solids can build up at the bottom. 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.
You want to ensure you have plenty of water in your black tank to break down any solids and help with dumping your tanks. If not, you could be frustrated with a clogged black tank.
Pro Tip: These tips on how to Simplify Black Tank Dumping with an RV Macerator Pump will change your RVing game!
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. It will minimize any gunk or debris from sitting in your black tanks while your RV is in storage.
However, if you’re traveling full-time in your RV, you’ll want to flush out your system every third or fourth time you dump your tanks. There’s no use in holding up the line at the dump station if it’s unnecessary.
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. A typical toilet will hold a gallon of water when at capacity, so this can take some time to accomplish. Be aware of others waiting to use the dump station. However, you don’t want to skip this step if you won’t use your RV for weeks or months.
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.
In addition to helping keep your black tanks clean, ample water in your tank can reduce the chances of clogs. When you open the valve to dump your tanks, gravity forces the solids and liquids out. The more water you have, the more force there will be to push any solids out of your black tank.
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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