Few things are more frustrating than checking your RV’s holding tank monitor only to see a reading that doesn’t make sense. A tank that says “full” when you just emptied it, or refuses to move past “empty”, can leave you wondering whether the sensors are dirty, damaged, or simply unreliable.
Thankfully, inaccurate readings don’t always mean you need to replace your RV holding tank sensors. In many cases, cleaning the tank and removing buildup from the sensors can help restore more accurate readings and get your monitor working properly again.
In this guide, we will show you how to reliably clean and restore black and gray RV tank sensors, and explain why replacing, rather than cleaning, RV freshwater tank sensors is the best choice.
Learn more about how RV holding tank sensors work with our guide: RV Holding Tank Sensors: How They Work and How to Clean Them
Key Points About Misreading RV Holding Tank Sensors
- Misreading RV holding tank sensors can be caused by debris covering the sensors, mineral deposits, wiring problems, or control problems.
- RV black tank sensors often misread when human waste or toilet paper is covering them or closing the circuit and causing them to misread.
- RV gray tank sensors typically misread when grease or oil becomes caked onto them, or when mineral deposits develop.
- We recommend using Unique Restore-It to clean RV black tank sensors, and Dawn Ultra dish soap for cleaning RV gray tank sensors. You may have to clean your holding tank sensors more than once to restore them.
What Causes RV Holding Tank Sensors to Misread?
RV holding tank sensors function as an electrical circuit where the rising water levels in your holding tanks complete the circuit and light up the corresponding level gauge. The lowest sensor in the holding tank is commonly called the “ground sensor” and the remaining sensors are installed in thirds or quarters above the ground sensor.
Holding tank sensors are particularly challenging to maintain because they are usually located on the deepest end of the tank near the discharge port, meaning that when you open the valve to dump the tank, all of the liquid, waste, and debris (toilet paper or food particles) is pushed to the wall where the sensors are positioned.
Debris
The most common reason that RV holding tank sensors stop working is when removable debris like human waste, toilet paper, grease, or food particles cover the sensor, hanging off of it into the liquid below.
When this occurs, the debris can complete the circuit, causing the sensor to falsely indicate that the water inside the holding tank has reached that level.
How does this happen? When an object that can conduct electricity is shorting the path of the circuit, it changes the resistance that the control board is looking for under normal conditions. This will cause the control board to display a misread of the liquid level.
If debris is the problem you’re dealing with, the problem can be fixed by cleaning the debris off of the sensors, allowing them to read accurately again.
Debris in Black Tanks
In black tanks, if toilet paper is caught on one of the black tank sensors and is hanging down into the liquid at the bottom of the tank, the circuit will close and show that there is liquid in the tank even if you just dumped the black tank.
Debris in Gray Tanks
In gray tanks, food debris can close the circuit between a sensor and the liquid in the tank.
However, it’s more common for a film of grease from food, soaps, shampoos, body oils, and other materials to stick to the holding tank wall where the sensors are positioned, which can make paths where water runs from the sensor to the liquid below and closes the circuit.
Mineral Deposits
Another reason RV holding tank sensors stop working is when non-cleanable mineral, calcium, or hard water deposits cover the sensor and prevent it from functioning properly.
Mineral deposits can often not be cleaned effectively, and sensor replacement should be considered.
Wiring Problems
RV holding tank sensors can also malfunction if there are wiring problems. For example, there might be a broken wire from a ring terminal, wire insulation could rub through causing the wire to ground, or the wire might be pinched.
In these instances, the damaged wire will need to be repaired or replaced to fix the problem.
Control Problems
Control problems are the least likely cause of RV holding tank sensor problems, but poor connection at the Molex connector to the circuit board, failed resistors, etc. can also prevent sensors from working.
If the control board has suffered damage, it will need to be fully replaced in order for your sensors to read correctly.
Garnet SeeLevel RV Holding Tank Sensors: A More Reliable Option
If you’re constantly dealing with misreading RV sensors, Garnet SeeLevel holding tank sensors have been available for aftermarket installation for over 30 years, and are still the most reliable, go-to sensors for RV holding tanks.
SeeLevel RV sensors are installed on the exterior of the holding tank, which makes them:
- Easier to install correctly.
- Less likely to misread as a result of internal tank debris.
SeeLevel holding tank sensors are now being installed by manufacturers on new RVs, typically for larger, high-end Class A, 5th Wheels, in addition to high-end Class B’s, and Travel Trailers.
Important Note: No RV holding tank sensors are perfect, and SeeLevel RV tank sensors can still be affected by damaged components or wiring issues.
Steps for Cleaning RV Black Tank Sensors
For black tank sensors, we recommend using Unique Restore-It, a product that utilizes bacteria and enzymes to clean and restore your sensors, ensuring accurate readings and a worry-free RV experience.
1. Close RV Black Tank Valve
Regardless of the type of camping you’re doing, you should always keep your black water tank valve closed unless actively dumping. Keeping your RV black tank valve closed helps prevent clogs, pyramid plugs, and foul odors in your camper.
Guide: Why It’s Crucial to Keep Your RV Black Water Valve Closed
2. Fill RV Black Tank With Water
Restore-It can only clean where water is touching, so filling your tank completely allows the treatment to clean your misreading sensors.
You can fill your tank (until water begins to back up into the toilet bowl) in several ways:
- By holding down your flush pedal.
- By using your onboard rinser (if your RV is equipped with one).
- By using a tool (like a hose, rinse wand, etc).
Be sure to monitor the toilet while you are filling the tank to make sure you don’t overflow the tank.
3. Shake Bottle of Unique Restore-It RV Black Tank Sensor Cleaner
Shaking the treatment bottle helps to make sure the ingredients are properly mixed and evenly distributed before being used.
4. Pour 16 Ounces of Restore-It Into RV Black Water Tank Through RV Toilet
Half the bottle is used at a time because some RVers need multiple treatments to completely restore sensor functionality. Each bottle contains two treatments for your convenience.
5. Allow Restore-It to Work for 12-72 Hours, or More!
There is no time limit for Unique Restore-It, and you can confidently let it sit for days, weeks, or months. In fact, the more time you give Restore-It to work, the greater your results will be.
Important Note: We do not recommend using the black tank while Restore-It is working!
6. Open RV Black Tank Valve and Dump the Tank
Always make sure to dump at an approved dumpsite.
7. Rinse RV Black Tank Thoroughly
Our preferred method of rinsing is filling your black tank completely full with clean water, and then dumping the contents. We recommend repeating this 1 to 2 times to most effectively rinse your black tank.
Important Note: This method is far more effective for thoroughly rinsing a tank than using internally mounted tank rinsers, tank wands, or external tank flushers. Our extensive testing of these external devices has proven that they are highly ineffective for the majority of RV wastewater systems. The only way to be sure you’ve drained all the remaining waste out is to routinely fill and dump your tanks.
Video: How to Rinse an RV Black Water Holding Tank
8. Close RV Black Tank Valve
Always keep closed unless actively dumping.
9. Wait 1 Hour to Allow RV Black Tank Sensors to Dry Completely
It is important for the tank to dry completely so you can rule out broken sensors or wiring problems.
When the holding tank is dry, there is nothing to complete the electrical circuit (because water is the conduit). This means that even dirty probes won’t provide readings in a dry tank.
10. Test RV Black Tank Sensors
Fill RV black water tank again to make sure the level gauge shows tank levels correctly.
If the sensors read correctly, dump the tank. You’re done!
If the sensors are still misreading after a second or third treatment with Restore-It, you have two options.
- We recommend trying again with Restore-It: Avoid the temptation to resort to chemicals. Some chemicals included in products like Drano can cause damage to seals, valves, and other components of your tank — we don't recommend using them.
- When your tank is verifiably empty and dry, check your sensors: If they read “full”, it is likely that you have a wiring issue or control board failure.
The restoration process is easy if your RV is sitting in your driveway not being used, but it gets much more challenging when full-time RVers are trying to clean black tank sensors and use the tank at the same time (refer to the Modified Sensor Cleaning for Full Time RVers section below).
Note: Refer to the guide on Full Time RVing: The Definitive Guide To Treating Your Tanks for more details on the best ways to treat your tanks while full-time RVing.
Modified Steps for Cleaning RV Black Tank Sensors: Full-Time RVers
If you’re a full-time RVer, cleaning your RV black tank sensors can be tricky when you’re trying to use your camper bathroom normally, especially when you may not have the ability to fill the tank completely with water (which is ideal for sensor restoration).
To restore black tank sensors while camping full-time, use these modified steps:
- Step 2 Modification: Only fill your black tank half way or three-quarters full (depending on usage).
- Step 4 Modification: Add one entire bottle of Restore-It to the black tank.
- Step 5 Modification: Continue to use your RV toilet normally, allowing Restore-It to work for 72 hours or more before dumping.
Important Note: It is always ideal to clean sensors while your black tank is not in use. This allows you to fill the tank all the way and allow the treatment to reach the highest sensors inside the tank. Attempting to restore black tank sensors while continuing to use your RV bathroom means that your results may vary.
Steps for Cleaning RV Gray Tank Sensors
For gray tank sensors, we recommend using Dawn Ultra dish soap because it is the best grease-eating dish soap on the market.
We even recommend using Dawn Ultra to clean your dishes because it will continue cutting grease inside your RV gray tank after every load.
Pro Tip: We suggest buying a large container of dish soap since you may need to repeat this process several times to fully clean the sensors.
1. Close Your Gray Tank Valve.
2. Fill Gray Tank Completely with Fresh Water and 20 Ounces (or more) of Dawn Ultra Dish Soap
While the sink is running, begin by pouring 20 or more ounces of Dawn Ultra dish soap down the drain. This will help ensure that the Dawn flows beyond the p-trap under the sink and into the gray tank.
Once the Dawn Ultra dish soap has been added, continue running the sink while monitoring the lower drain that feeds into the gray tank (typically the shower drain). You will know the tank is full, or nearly full, when you see soap suds backing up the drain pipe.
Filling the tank as much as possible is essential because sensor cleaning only occurs where water is touching, so make sure that water covers the highest (“full”) sensor in your gray tank.
Important Note: There is no amount of Dawn Ultra that is too much. You may see the soap foaming back out of your sink or shower lines — an indication you’ve poured enough Dawn into the tank —- which is a good sign. This lets you know that the grease-eating dish soap is actively spreading throughout your RV’s pipes and cleaning out all the built-up residue.
3. Let Dawn Ultra Work Overnight
Allowing Dawn Ultra to work overnight allows it to fight tough grease in your RV pipes and gray tank.
4. Open RV Gray Tank Valve & Dump the Tank
If you are using a clear fitting or sight glass fitting connected to the sewer hose (which we recommend when dumping), there is a good chance that you’ll see gray or white residue on the bottom of your RV holding tank discharge pipe. This is the grease that was previously clinging to the inside of your holding tank.
Always make sure you dump at approved dumpsites: Where to Dump Your RV Holding Tanks
5. Wait 1 Hour to Allow RV Gray Tank Sensors to Dry Completely
It is important for the tank to dry completely so you can rule out broken sensors or wiring problems.
When the holding tank is dry, there is nothing to complete the electrical circuit (because water is the conduit). This means that even dirty probes won’t provide readings in a dry tank.
6. Test RV Gray Tank Sensors
Fill the RV gray water tank again to make sure the level gauge shows tank levels correctly.
If the sensors read correctly, dump the tank. You’re done!
If the sensors are still misreading, repeat this process the next night, repeating this process until sensors are restored to proper functionality. If after the second of third cleaning with Dawn Ultra, the sensors are still misreading:
- We recommend trying again with Dawn Ultra, and avoid resorting to chemicals. Some chemicals included in products like Drano may cause damage to seals, valves, and other components in your RV holding tanks.
- When your tank is verifiably empty and dry, check your sensors. If they read “full” it is likely that you have a wiring issue or control board failure.
If you want more information about which RV cleaning products are safe, and which ones you should avoid, refer to our guide: Choosing the Right Products or Methods for Cleaning RV Tank Sensors
Modified Steps for Cleaning RV Gray Tank Sensors: Full-Time RVers
Full-time RVers can use the same process for cleaning their gray tanks that we have outlined above.
However, it’s important to remember that Dawn Ultra can only clean sensors they can reach; sensors not touched by water cannot be cleaned, so results may vary when tanks aren’t filled completely.
Steps for Cleaning RV Black/Gray Combo Tank Sensors
Cleaning and restoring your black/gray combo tank effectively depends on how you’re using it:
- Black Water Only: Refer to our Steps for Cleaning RV Black Tank Sensors
- Gray Water Only: Refer to our Steps for Cleaning RV Gray Tank Sensors
How to Clean & Restore Black/Gray Combo Tank Sensors
If you’re using your combo tank for both black and gray water, we recommend the following:
- Start by following the Steps for Cleaning RV Black Tank Sensors: If after following these steps your sensors are still misreading, you may either need to repeat the cleaning procedure for black tank sensors again, or move onto the gray tank cleaning method.
- If your sensors are still misreading, follow the Steps for Cleaning RV Gray Tank Sensors: If grease and oil are caked onto your RV combo tank sensors, Restore-It (used for black water tanks) won’t be able to clean it very well, which is where Dawn Ultra dish soap becomes a better solution.
- If your sensors are still misreading after repeating both processes several times: Your RV combo tank sensors may need to be repaired or replaced.
Why You Should Always Replace RV Freshwater Sensors
RV freshwater holding tank sensors typically fail because of hard water or mineral deposits. Less frequently, these RV tank sensors can also misread because of wiring or control problems.
When enough mineral deposits build up on the RV fresh water tank sensors, they become insulated from the water and no longer close the circuit, causing the sensors to misread.
Mineral deposits, mainly calcium, lime, and magnesium, are difficult to remove from RV fresh water tanks because they cause hard, stubborn scale to form that bonds to plastic surfaces over time.
Mineral buildup requires strong, acidic cleaning solutions to remove, and harsh chemical cleaners can cause the following issues in RV fresh water tanks:
- Damage to Rubber Seals & Valves: Acids and chemicals can dry out and destroy RV components, and when pumped out of the tank can cause damage to the water pump, fittings, and other gaskets.
- Increased Sensor Malfunctions: Acids can damage, dull, or pit the plastic and metal components of RV fresh water tanks, causing sensors to give incorrect readings, or completely fail.
- Environmental Hazards: When harsh or acidic cleaners are dumped into campground septic systems, they can kill the microbes necessary for sewage treatment, leading to environmental harm and potential system failure.
- Creates Toxic Gas: Mixing acid-based cleaners (vinegar or certain toilet bowl cleaners) with bleach can create toxic chlorine gas, which can be dangerous in the confined living space of an RV.
Rather than attempting to clean RV freshwater tank sensors, the recommended solution is to replace them.
What are the Benefits of Replacing RV Freshwater Tank Sensors?
Replacing faulty sensors in RV freshwater holding tanks is preferred for the following reasons:
- Cost Effective: RV water tank level sensor replacement is the most cost-effective option, because RV tank sensors are relatively affordable.
- Long-Term Results: Attempting to clean sensors with mineral buildup is rarely effective, and even if you are successful, you’ll need to repeat the process frequently. Replacing the RV water tank sensors gives the most reliable and long term results.
- Prevents Damage: Attempting to clean stubborn mineral buildup is very difficult, especially without the use of acids or other harsh chemicals that can damage your RV holding tank and its components, particularly the bushings. Once removed, the bushings that are designed to expand and close gaps around the sensors become deformed, making them difficult, or nearly impossible, to reinstall without causing further damage.
- Maintenance Opportunity: Replacing the RV water tank sensors also gives you the opportunity to check all of the wiring connections, and tighten them if necessary. We also recommend checking the RV water pump filter for build up on the screen, and replacing it if necessary (the freshwater pump is typically located close to the RV fresh water tank).
For full instructions about how to replace RV freshwater sensors, read our guide: How to Fix Fresh Water Tank Sensors
How to Prevent Misreading Sensors With The Unique Method
The Unique Method was carefully developed over decades of working with RVers that are struggling with odors, clogs, and misreading sensors.
The core of The Unique Method is a 50/50 approach: 50% following the right process, and 50% using the right product.
While there is no magic solution, those who follow The Unique Method, using both the right process and the right products, can experience the best that RVing has to offer.
However, if you opt to use an ineffective product but still follow the process, or if you use an effective product, but don’t follow the process, the reality is simple: problems are sure to follow.
Trusting The Unique Method is easy — all you have to do is make minor adjustments to your daily habits regarding RV holding tank care practices and treatment products to see the incredible results. Make your RVing dreams a reality with Unique Camping + Marine.
Learn more with our guide: How to Prevent False RV Sensor Readings
Get Help With Misreading RV Holding Tank Sensors
If you’ve been following along with our guide and you’re still struggling with your RV holding tank sensors, don’t stress! Reach out to the professional Customer Service Team at Unique Camping + Marine for expert advice about your RV holding tank sensors. Whether you have a quick question that needs answered, or you’re dealing with a massive RV holding tank problem, our team is ready to help.
Frequently Asked Questions About RV Holding Tank Sensors
Below we’ve put together a list of the most frequently asked questions about RV holding tank sensors, giving you answers in one convenient location.
1. Why Do RV Holding Tank Sensors Misread?
Misreading RV holding tank sensors can be caused by debris covering the sensors, mineral deposits, wiring problems, or control problems.
2. How Do RV Holding Tank Sensors Work?
RV holding tank sensors function as an electrical circuit where the rising water levels in your holding tanks complete the circuit and light up the corresponding level gauge.
3. Can I Clean RV Holding Tank Sensors Myself?
Yes! You can clean RV holding tank sensors by filling your holding tank with fresh water in combination with a high-quality sensor cleaner (Unique Restore-It for black tanks) or grease-eating dish soap (Dawn Ultra for gray tanks), allowing the treatment to clear off stubborn debris, and thoroughly rinsing the tank afterwards. You may have to clean your holding tank sensors more than once to restore them.
4. What Products Should I Use to Clean RV Holding Tank Sensors?
We recommend using Unique Restore-It to clean RV black tank sensors, and Dawn Ultra dish soap for cleaning RV gray tank sensors. You may have to clean your holding tank sensors more than once to restore them.
Important Note: Avoid using harsh household chemicals, bleach, or standard drain cleaners, as these products can damage tank seals, valves, and plumbing components.
5. How Often Should I Dump & Clean RV Holding Tanks to Prevent Sensor Problems?
You should dump your tanks every 3-5 days for optimum odor control and clog prevention, thoroughly rinse your holding tanks every time you dump, and deep clean your RV black tank twice per year with Unique Clean-It (season beginning and end for weekend campers) or every 5-10 dumps (for full-time RVers).
6. Do RV Holding Tank Sensors Break, How Can I Tell?
Yes! Dump your RV holding tank completely, and allow the tank to fully dry. When your tank is verifiably empty and dry, check your sensors. If they read “full” it is likely that you have a wiring issue or control board failure.
This method is effective because if your holding tank is dry, there is nothing to complete the electrical circuit because water is the conduit. This means that even dirty probes won’t provide readings in a dry tank.
If your sensor panel shows water levels in the tank, even in a 100% completely dry tank, that is a surefire way to know that you’re dealing with a wiring problem or failed control board.
7. Can I Upgrade My RV Holding Tank Sensors With Something More Reliable?
Yes, aftermarket sensors like SeeLevel RV Tank Sensors are a great option if you want more reliable readings on tank levels. This is possible because having sensor probes positioned outside of the tank means that waste and grease cannot stick to the sensors and cause them to misread.
8. How Can I Prevent Misreading RV Holding Tank Sensors?
You can help prevent misreading RV holding tank sensors by following The Unique Method.
After 30 years of solving wastewater issues professionally, Unique Camping + Marine developed these easy-to-follow guidelines for effective odor elimination, solid waste breakdown, and effortless sensor cleaning.
9. Why Do Gray Tank Sensors Misread if the Tank Only Holds Sink & Shower Water?
RV gray water holding tanks accumulate soap scum, grease, oils, and even mold and mildew from shower and kitchen wastewater. This film can coat the holding tank sensors, leading to inaccurate readings over time.
10. Do Extreme Temperatures Affect RV Holding Tank Sensors?
Extreme tank temperatures are not the primary cause of RV holding tank sensor malfunction, but temperatures above or below the ideal tank temperatures of 45-85°F [7-29°C] can cause contents to dry out or freeze faster, resulting in debris sticking to sensors and tank walls.
