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How to Clean RV Holding Tank Sensors (Black + Gray Tank Sensors)

Written by Stephen Ryan / Fact checked by William Turner

how to clean rv holding tank sensors

Are you wondering whether your tank is already full of gunk or not? Learning how to clean RV holding tank sensors can save you the hassle of a smelly motorhome because of overflowing liquid and human wastes.

Getting gunk on your sensors can lead to faulty readings. The devices will not alert you if the holding tank is already full. A dirty gray or black water tank sensor can produce a smelly problem that makes your RVing less enjoyable.

That is why cleaning these sensors is an essential skill for all motorhome owners. What you need to do first is to choose a suitable cleaning agent for your kind of tank, before proceeding with the cleaning steps.

Table of Contents

Things You Will Need to Follow This Tutorial


There are a couple of things you must know to clean RV tank sensors.

Knowledge of Black and Gray Holding Tanks

Your motorhome has three water tanks: freshwater, gray, and black. The freshwater tank accommodates the water you use during your travel, including food preparation, dishwashing, bathing, toileting, and more.

On the other hand, the others hold wastewater. The black holding tank connects to your toilet and collects stool, urine, and other materials you flush down the lavatory.

The gray one accommodates wastewater other than that coming from the toilet. It can include water draining from the kitchen sink, bathroom drain, bathroom sink, and other fixtures.

Because the RV holding tanks accommodate wastewater, there is a chance grease and gunk can form on the sensors. These materials coat the devices, causing them to fail. That is why it is essential to clean the entire tank to remove the gunk in these sensors.

Cleaning Agents

The black holding tanks require a more powerful cleaning solution. You can use an enzymatic agent to break down microorganisms and other organic matter in the black holding tank. These products contain potent substances that dissolve organic materials and kill microorganisms.

For your gray holding tank, an ordinary dishwashing detergent is sufficient. However, many RV manufacturers and owners recommend dish soap with grease-cutting capabilities. Oil from your cooking pans can drain into the holding tank and coat your sensors with grease.

You can also use an RV tank cleaning wand, which is almost similar to a high-pressure power washer with a long spray neck. This cleaning tool is beneficial in cleaning the black holding tank’s sidewalls.

A high-pressure water spray will also work to rinse your RV holding tanks.

How to Clean RV Holding Tank Sensors (Black Tank Sensors)


Step 1. Park Your RV in the Right Location

Always park your RV in an area where there are few people around. It would also be best to park it near a water supply source because you will fill the holding tank with water for cleaning. Access to a drainage system is also a must since you will be removing the nasty contents of your tank.

Pro Tip: It would be best to park your motorhome in a campground with waste dumping facilities. Cleaning black tank sensors is a messy and smelly business since the tank contains human wastes.

Step 2. Drain and Close the Black Holding Tank’s Valve

Open the black holding tank’s valve to drain its contents into an appropriate vessel or compartment. Check the campgrounds if they have a facility to accommodate such wastes.

Make sure to empty the tank before closing the valve. If you are not sure how to do this, refer to the owner’s manual.

Ask a Trucking Recruiter has a fascinating video on how you can empty your RV black and gray holding tanks.

Once empty, close the shutoff valve.

Step 3. Fill the Holding Tank with Water

Connect your holding tank to a city or municipal water supply and fill it with water. Ideally, you will want to fill the tank up to the highest sensor level, which you can almost always find near the top of the holding tank.

If the holding tank does not have an inlet port, you might want to flush your motorhome toilet several times. The water will go straight to the holding tank. If you go down this route, it would be best to fill your RV’s freshwater tank.

RV with Tito DIY has a mind-blowing video about how you can refill your motorhome’s freshwater tank without using your RV’s water pump.

Step 4. Add Your Chosen Cleaning Agent

Next, add your cleaning agent. Ensure to use the correct concentration to achieve maximum cleaning effects. You might want to read the cleaning solution’s recommended usage and adjust your formula accordingly.

Some cleaning products require you to leave them in the holding tank for up to 72 hours. The long treatment period is necessary for killing microorganisms and dislodging nasty substances from surfaces.

If you are using enzymatic formulas, you need adequate time for the product to break down organic molecules in your holding tank.

Step 5. Clean the Holding Tank

The next step in RV black water tank sensor cleaning is draining it. Get your tank cleaning wand and connect it to a water supply using a garden hose. Bring the wand inside your motorhome and into the bathroom.

Open the RV composting toilet by pushing on the flush lever and insert the cleaning wand straight into the holding tank. Start cleaning the tank’s bottom, working your way up. Pay attention to the tank’s sidewalls. It will help if you move the wand in a circular motion to ensure a more thorough cleaning.

Pro Tip: Using a high-pressure power washer can help you clean the tank more effectively.

Step 6. Rinse the Holding Tank and Repeat Steps 3 to 5 If Necessary

Open the drain valve and empty the tank. After draining the tank, close the valve again and refill the black tank with water. You might want to use the cleaning wand or a power washer to rinse the tank thoroughly.

If the water return is not as clean as you want, you can repeat the process from Steps 3 to 5.

How to Clean RV Holding Tank Sensors (Gray Tank Sensors)

Cleaning the gray holding tank follows the same steps as removing gunk in a black holding tank sensor. However, the difference is that the source of water will come from your kitchen and bathroom faucets and showerheads.

Step 1. Close the Gray Holding Tank Valve

Your gray holding tank is not as dirty as the black unit because it only accommodates wastewater from sources other than your camper toilet. You do not need to observe a 72-hour disinfectant period for this. Eight hours of standby time should be enough.

That is why it is best to drain your gray holding tank right before you go to bed. Once done, you can close the tank’s valve.

Step 2. Fill the Holding Tank with Water

Open all faucets and showerheads to fill your holding tank. It will be wise to fill it up to the topmost level – the full holding tank sensor’s location.

Always note your holding tank’s capacity because it will help determine the amount of cleaning solution to add in the next step.

Step 3. Add Your Cleaning Agent

You do not need a powerful RV tank sensor cleaner for this. An ordinary cleaning solution made of water and dishwashing detergent is sufficient.

Some RV manufacturers recommend pouring at least 20 ounces of eco-friendly dish soap, such as Blue Dawn, down your kitchen or bathroom sink or the shower drain. You might see foam formation. Do not freak out because this is normal.

Foam production is always a good sign that the dish soap is breaking down grease and gunk in your drain lines.

Leave the dish soap to do wonders in your holding tank and go to sleep.

Step 4. Clean the Gray Holding Tank

When you wake up the following morning, it is time to clean the holding tank. Open the tank valve and drain the contents. You should see a whitish to grayish residue at the tank’s bottom – a sure sign that the dish soap worked its magic.

Too bad you cannot use an RV holding tank cleaning wand for this. What you can do is use a pressure washer to spray a powerful water stream through your kitchen sink or bathroom drain.

Step 5. Rinse the Tank Well

Continue dumping your holding tank’s content and refilling it with water by opening all RV faucets and showerheads. Ensure to close the valve every time you top up the tank and open the valve when draining.

It would take several cycles to get the job done.


You do not have to live with faulty sensor readings and leave you at the mercy of a smelly holding tank. Learning how to clean RV holding tank sensors will help you regain control of your delightful RVing adventures, freeing you of foul-smelling tanks and ensuring well-functioning sensors.

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