Your RV Holding Tank Sensors Explained

Why Do I Need RV Tank Sensors?

You only need (need is a strong word) RV tank sensors when you dry camp.

Contrarily, if you camp ONLY in campgrounds with full hook-ups, you do not need tank sensors. Why? Because you'll always be connected to utilities so you don't use the tanks.

The job of a holding tank level sensor is reading how empty or full the tanks are. When you're connected to water and sewer, there's no need to fill any of your tanks for long or at all.

You benefit more from holding tank sensors if you camp without utility connections.

Because now you are self-contained. You store your wastewater inside your waste tanks. They are only so large.

Therefore, you want to know when they are getting close to empty (freshwater) or full (gray and black) so you don't run out of water or overflow your toilet or sinks/shower drain.

Let's dive a little deeper into why you don't need to use your waste tank sensors when you are in a campground with full hook-ups.

Then, the water coming into your RV goes directly into the pipes, bypassing that holding tank.

Therefore, there's no filling of the tank and no need to know how much is in there.

Black Tank:

You also don't NEED your black tank sensors to tell you when your toilet tank is full.

You can either dump your black tank once a week or so, or you will 'see' or hear when it's time.

How will you see or hear it? Because your toilet either won't flush anymore, or it will 'burp' before that time comes, and boom, you know it's time to dump.

When Do You Need To Use RV Holding Tank Sensors?

RV tank sensors are helpful when you are camping without full hook-ups, meaning when you are dry camping.

When camping like this, there's no water or sewer connection.

Therefore, your freshwater tanks hold the water you need for washing dishes, showering and that you rinse stuff with.

Your gray tank collects and holds that waste water. Your black water holding tank collects and holds the toilet water.

Now your sensors are handy to tell you when they are getting (freshwater) close to empty or getting close to full. When that time comes, it's time to dump and fill.

These capacitive sensors also give far more accurate readings of the tank levels, displaying the levels in a percentage. They will show an accuracy of around 8%, which is a lot better than a probe sensor setup.

You will typically find this style of a sensor on upper-end recreational vehicles.

Great as that sounds, it's a flawed design, as things other than liquids can get caught on the other side of the sensor, causing a misread.

This includes toilet paper, struvites, food particles, grease, etc.

The issue is not necessarily a sensor problem. Instead, the RV tank sensors may work just fine.

It's that there is debris caught inside the tank causing the monitor to display a false reading.

To take proper care, be sure to use toilet paper safe for RV use (better yet, don't flush your paper at all), and try to keep as much dishwashing waste (food debris and grease) from going down your drain.

There is a style of RV water tank sensor that mounts to the outside of the tank and uses electronics to measure the capacitive difference in liquid levels inside the tank.

This system is much more accurate than a traditional probe-style RV water tank level sensor but costs more, so you will typically only see it on higher-end RVs.

However, these exterior mounted RV tank gauge sensors don't collect debris like internally mounted sensors and therefore are practically immune to showing false readings.

How Do You Read An RV Tank Monitor?

To read your RV tank monitor, first, you must locate yours. Some are displayed out in the open. Others are behind a cabinet door.

The monitor panel has a display that is very simple to read. Some give a percentage full; others give '1/2 full, 3/4 full,' etc.

Some are digital, and others have lights that come on next to a level when you select to see how empty or full a tank is.

RV tank monitors are very simple to read. You most likely will need to press a button to display the reading, and each tank may have its separate button.

How Do You Clean The Sensors On An RV Holding Tank?

Cleaning the sensors on an RV holding tank of goo or debris may be a little tricky. It's likely easiest in your black tank. But we shall cover both the black tank and the gray tank.

(Freshwater tank sensors rarely get contaminated with anything if you only put water into that tank, as directed.)

Read on to find out how to clean RV holding tank sensors.

How Do You Clean Grey Water Tank Sensors

You may need to clean your grey water tank sensors if they get blocked by soap scum, grease, or other residue and debris buildup on the tank walls.

To fix it, the offending stuck residue or buildup causing a reading problem needs a rinse from the walls to clear that sensor.

We believe the first method here to be the most effective solution. But you could try the dishwashing liquid treatment first since it is cheaper and you might have the right soap on hand.

1. We like the Unique Sensor Cleaner product. It uses bacteria to dissolve all of the solids in a tank. To use, fill your tank to FULL. Add treatment. Leave at least 12 hours for everything to dissolve. Drain. Check sensors. If still reading incorrectly, repeat.
2. You might try a dishwashing liquid first as a deep clean per the instructions found here. For some, this works as an effective solution.

There's a product called the Camco Flexible Swivel Stik. This works if your toilet is close to the tank.

The product has a bendable stick, so even if your drain line has a bend in it, the tip can reach down into your tank.

Connect it to a garden hose and let 'er rip! Be VERY CAREFUL that you don't let the tank fill up and overflow.

Best to do this procedure when connected to a ground sewer outlet so you can open the RV waste valve assembly for your black water holding tank.

This way, you cannot overflow the tank into your RV. Allow the sprayer to clean while you lower and lift the device, so you get as much coverage on the walls as possible.

Then, remove, and test your monitor and tank sensor to see if you get a correct indication.

Black Tanks

Your black tank offers two ways to know you're close to being full sans the holding tank sensor. 

I haven't bothered with seeing how my black tank monitor reads for years now. Instead, I rely on these two things:

1. You learn how long you can go on a trip before needing to dump. It stays consistent if your habits/number of people using it doesn't change.
2. Your toilet(s) will announce when they are almost full. Once the sewage level starts to creep up the pipe leading from the toilet down into the tank, it will 'burp' when you flush. You'll notice it. Hard to miss this sign that your tank is very close to being full.

If yours does have the holes, here's how you calibrate:

Fresh Tank:

This is the easiest one.

1. Fill your tank with water.
2. Go inside, push fresh water tank button.
3. Insert a screwdriver into the hole above the fresh button.
4. It should read full. If it doesn't, turn to the right until it glows full.
5. If it shows full, turn it slowly to the left until it turns off.
6. Then turn it right until it glows red.

Gray Water Holding Tank

Do you really want them to have ZERO room to spare when they read full?

If you want a little bit of wiggle room, keep this in mind when calibrating.

1. Fill your grey tank until the monitor says it's 3/4 full.
2. Next, add water down your shower drain until your monitor reads full.
3. If you want it to show only when it's ABOUT to overflow, fill until you barely see the water creeping up towards the drain.
4. There, calibrate the monitor to say full.
5. If you want more wiggle room, once you see the water rising, dial it forward (to the right) until it is 'over' full.

Black Water Tanks

Do this the same way you did the gray tank sensor if you want some wiggle room to know you can still go a day or so once it hits your holding tank level indicator hits the full mark.

Best to do this when connected to a sewer. (But NOT while at a dump station.)

1. Fill tank until it reads full.
2. As soon as your black tank says full, start adding water in one-gallon amounts at a time. And count the gallons.
3. This will let you know how many gallons are truly left once it says full.
4. Once you can see the liquid when you open the toilet flap, you've reached the number of gallons you had remaining.
5. If you want more warning time, dial the sensor back a touch. If you wish for less warning time, dial it forward a little.

RV tank sensors aid RV owners in knowing how full or empty their tanks are.

Though people can live without them, they help keep track of your tanks when you're dry camping.

That said, the gray tank and RV black tank sensors often give incorrect readings at the monitor panel due to blocked sensors.

Sensor issues are pretty easy to resolve by using an RV sensor cleaner.

If you only camp with full hookups, you'll rarely need to use your RV tank monitor system.

But when you do dry camp, you'll be happy you have an RV tank level sensor in every tank!

If you regularly use an RV holding tank sensor cleaner, you're less likely ever to have problems with your RV holding tank monitor system.

If they don't work, don't let that stop you from getting out there and camping! Your RV tank monitor panel and sensors are a luxury, not a necessity!