Friday, September 22, 2023


Ask Dave: My holding tank gauges never work. Is there another option?

Dear Dave,
Since the holding tank gauges that detect the levels in the various liquid tanks are so error-prone, what exactly is the gauge? What does it look like? How does it work? How is it replaced? Are there other systems being investigated/researched to make better gauges? Thanks. —James, 2020 Coleman 2515RL

Dear James,
The level gauge inside your rig shows the level in your black water, gray water, and fresh water tanks. The information is provided by a series of sensors in the holding tanks. Typically, there is a main 12-volt positive wire that runs to the 1/4 or 1/3 level on the tank, depending on how your gauge reads. A hole is drilled in the tank and the sensor is inserted and the screw tightened. This pulls or sandwiches a rubber gasket (similar to how a pop rivet works) and a rounded metal probe or sensor is inside the tank wall.

Then, another sensor is positioned about 6-8 inches directly across from the main power sensor and that is wired to the gauge inside. Another is slightly higher at the 1/2 or 2/3 level, and then 3/4 and full. When the fluid in the holding tank rises, it will provide continuity or allow the power to pass from the main power sensor to the lowest and up as it fills.

The challenge with this type of sensor is the material that can collect on the sidewall of the tank and still create continuity or false readings as the tank is drained. A good black water tank flush valve can help clean off this material, but it’s not always a perfect solution.

Stick-on monitoring system pretty foolproof

Several manufacturers of Class A units have gone to a stick-on monitoring system that uses a micro-electrical field rather than fluid creating continuity. They have been pretty foolproof. Winnebago calls its system TrueLevel and uses Mirus sensors. You can purchase this system from a Winnebago dealer but will probably need to swap out your monitor panel control board.

Another product is called the RecPro RV Water Tank Monitor System, which can be found on Amazon here.

The product comes with three sets of sensors, with three used on each tank. It also comes with a proprietary gauge and 15’ of wiring. It’s a very inexpensive option and looks to be easy to install. You just need to find a way to get the wiring up inside the rig to the location you want the gauge.

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Ask Dave: Black water tank is clean but there are still smelly odors. Why?

Dear Dave,
After flushing the black water tank, there are still smelly odors like a sewage smell in the bathroom that seems to come from under the sink in the cabinet. I flush the waste tank until the water comes out clean and there is still a strong smell. Is there a one-way valve or something like that that may be stuck open? Thanks. —Luis, 2020 Winnebago Micro Minnie 1706FB

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Dave Solberg is a leading expert in the RV industry and the author of the “RV Handbook.”

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Dave Solberg
Dave Solberg
Dave Solberg is a leading expert in the RV industry and author of the “RV Handbook” as well as the Managing Editor of the RV Repair Club. He has been in the RV Industry since 1983 and conducts over 15 seminars at RV shows throughout the country.


  1. In my experience the SeeLevel Sensors and Monitor are reliable and have increased measurement resolution, with the self adhesive external sensors. New last year was the addition of a Bluetooth system. There are some limitations, as tank design (primarily corners and distance from denser objects like plumbing ports and metal framing) can interfere with measurement. I used painters tape to attach the sensors to the tanks, to verify functionality. Then attached the sensors permanently.

    Not the cheapest option for measuring tank level. But as with most things, you get what you pay for. Garnet 709-BTP3 SeeLevel II Tank Monitoring System with Bluetooth ( $360.

  2. I had the same issue with inaccurate readings from my black water tank. I saw a possible remedy on another forum and gave it a try. After my black water tank was empty and I had added the chemicals in dumped probably half to three quarters of a small bag of ice thru the toilet into the black water tank. The movement of the ice as you drove; before it melted; was supposed to loosen any stubborn deposits. It worked for me.

  3. I had See Level. Worked like sonar I guess. Very accurate but my black tank was wide and thin so when you flushed the water had to spread rather than rise. Took some getting used to but by filling with a bucket and writing down results we had a good system

  4. Horst Miracle Gauge is my choice. No electrical requirement.

    Relatively complex installation though since it uses air lines instead of electrical wiring.

    Measures actual depth of liquid in 1/8″ increments which is far better resolution than any other system out there.

  5. I have read nothing but good reviews of the SeeLeveL system. I plan to install that in my motorhome.

    I currently have a worthless 1/3, 2/3, F system. Even if it worked it’s not useful with those big measurement jumps.

  6. SeeLevel Tank Level Systems by Garnet is the ONLY way to go. You won’t be disappointed. Forget wasting money on any of the other brands.

  7. Winnebago used SeeLevel in their class C’s as well for a long time. Our 2008 has it and still works like a charm.

  8. I agree with Scott, Seelevel gauges are expensive, but work well. Mine were accurate for 7 years on my fiver with no problems. They read in percentages rather than 1/3, 2/3 and full. And you can parallel panels so you have one panel inside and another outside near the dump valves.

  9. SeeLevel gauges are not inexpensive but work fantastically well, and the customer support is very good. In their case (and I would guess others’) you can use the existing wiring from the tanks to the panel location.


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