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RV Holding Tank Indicator Not Accurate

by Dave Brimlow
()

How to Fix an Inaccurate Holding Tank Monitor

After we dump both holding tanks on our '93 Rockwood Bayport, the indicator panel still shows holding tank #2 2/3rds full. Is there a valve we're missing? I have found 3 - one under the shower, and the two at the discharge station.

ANSWER: No you have not missed a dump valve. It sounds like your RV holding tank gauge is the culprit. This is a common problem for a lot of RVers. The gauges not showing the proper level in your holding tanks could be due to the probes used to measure the waste level in the holding tank being dirty which causes them not to work. The first thing you can try is some RV Probe Cleaner and see if that gets the probes working again. Do not use probe cleaner in your fresh water tank.

Other RVers have had good luck by dumping some original Dawn Liquid Dish Detergent in their Black and Grey Water Holding Tanks. The Dawn seems to break up all of gunk on the probes. Again, do not use the Dawn in your Fresh Water Holding Tank.

Sometimes dumping a couple bags of ice cubes into the holding tank and driving the RV around will help clean the probes.

If none of the suggestions above work, there could be other problems causing the gauges not to work, such as a bad sending unit, a bad gauge, etc. In those cases you would have to have a Certified RV Technician diagnose and repair the problem.

Some RVers just give up on the tank gauges ever giving accurate readings and have become pretty good at just knowing when to dump the tanks.

Hope this helps.

Do you have any suggestions or comments on this topic? You can add them to this page by clicking on the "Click Here To Post Comments" link located near the bottom of this page.

Happy RVing

RVing Al

Comments for RV Holding Tank Indicator Not Accurate

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gunk on the sensors
by: Anonymous

RID-X
I purchased a used motorhome and the black water tank always said full. I tried everything but nothing seemed to work. Finally I tried treating it like a septic system. I filled the tank full of water and then added a packet of RID-X. I let it all sit about a week the dumped the tank. This did the trick. The sensors now accurately report tank level. I now make it part of my end of season procedure. I hope this helps.

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Holding tanks
by: Ted

The sensor systems are very poor. Probably the best system would be one that works like a stud sensor. As the level in the tank increases the frequency would decrease in the sensor and it would detect the correct level. (This is somewhat oversimplified but the idea is correct.)

To keep things simple, the freshwater sensors are usually reasonably correct depending on the resolution of the sensors. (I.e. 1/3, 2/3, empty or full)

I try to put the rinse water from the dishes into the black water tank. Then I know when I am out of water, my tanks need to be dumped. My tank capacities are: 80, 60, and 40 for fresh, grey, and black.

I do not leave my tanks connected to the sewer outlet in an open mode and I never use the fresh water from the campsite until I need to fill the fresh water tank.

Simple, inexpensive, and it just works.

Ted in Mexico with Monaco Monarch.

Rating

Inaccurate sensors
by: Anonymous

This unit is new, destination trailer, has never been trailered, never been wintered and is parked on permenant site, yet the first dump and cleaning indicates that the tanks are still 2/3 full. No waste material or paper have been placed in the black or gray tanks

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There should be a proceedure to reset the panel
by: Anonymous

My RV has a sequence of buttons you hold to calibrate the level sensors. What you do is empty the water/grey water/black water tanks and fill the propane tank. Then you push and hold respective button and it resets the computer.

For instance, my water tank was reporting 1/4 tank when it was full (I just filled it until water came out of the filler). I pressed in and held down the water button until it sequentially lit the LEDs until "F" was lit. Now it accurately reflects the water level. I would suggest you find out what panel you have and search for the manual on the internet. Some you can hold the button and others you have to turn a little recessed screw to set the correct level.

Hope that helps.

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bucket list
by: Marcus Fell

In 1987 I bought a new holiday rambler alumi-lite the tank gauges have never worked, this is a quality coach, I cant understand Holiday putting such a junk system in such a nice motor home, they have showed full regardless of level since day one, if anyone can tell me the problem I would sure appreciate it, regards Marcus.

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It's not rocket science
by: Anonymous

Seriously, it's not difficult to figure out how often to dump and just quit worrying about the sensors. I've tried the ice trick and it didn't work at all for me. Since I travel alone I know I can usually go about 10 days-2 weeks between dumping the black tank. You can also just use a flashlight and look down the toilet. It actually dumps better when it is very full.

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RV Holding Tank Indicator Not Accurate
by: Anonymous

I own a coachmen catalina and I get the same error reading on my test panel after emptying the black (sewage) tank; you can purchase a yellow banana wand (I call it) from an RV supplier, less than 10.00; you hook the wand up to a water hose and place it just under the toilet opening into the tank; the water pressure spins the wand-head which has openings to swirl any sludge away from the sensors. Something you usually have to do each time you empty your tank. After rinsing the top of the tank, this should show an empty reading.

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Skip the worries
by: Fomentous

Sensors get dirty. They would take time from my fun to clean. I'm used to my rig. I just dump all the tanks every 4 days and skip the worries. Your schedule may vary from mine. Have fun now. You'll be dead a long time.

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Holding tank indicator fix
by: Anonymous

Tank sensors are nothing more than a rubber gromet with a piece of metalgoing through it with a lug to attach a wire. There are four sensors that are drilled through your tanks at the 1/4, 1/2, 3/4, and full levels. A wore runs from each sensor to the coresponding LED light on your monitoring panel. The are typically two more sensors connected by a fith wire to the monitoring panel. when you push test voltage is sent down the fith wire and the circuit is completed by any sensors that are touching liquid. More than likely someone worked on it and got your wires mixed up. If you can find where they connect to the tank have someone watch the panel as you touch each wire to the positive lead and see which light lights up, then hook it to the proper lug. If the 3/4 light lights up then it goes on the 3rd from the bottom.

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Inacurate holding tank indicator
by: Anonymous

On your next trip out, fill the holding tank about half full, stop at a convenience store and buy a couple of bags of ice and dump in the toilet and go on down the road. The natural sloshing of the liquid in the tank along with the ice cubes in it will knock any debris from the sensors in the tank that record full level. When you stop at a dump station, empty the tank and check the gauge. Bet it will show empty. Neat trick and it works. May have to do this more than once if there was a lot of debris in the tank. repeat peroidically.

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water tank drain location on 2000 dolphin 36' motor home
by: John

For 2 years I have been looking for the fresh water tank drain on a 2000 36' Dolphin Motor Home. Because I could not find it I drained it by removing the water heater plug and letting the pump do the work. By accident I found it hiding behind some rolled up coax cable . It is located in the compartment with the fresh water valves, to the far right of the compartment there is a small opening that reveals the drain, it is pretty well hidden. Hope this helps.

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Electrosense Holding Tank Monitors
by: Chris Ferro

Bad tank monitors are a perennial problem in the marine and RV world, which is why we at Electrosense exist! I won't go into how and why our monitors are more reliable and durable (and easy to install) than most stock RV tank monitors, but you may at least want to take a look at them. We have a website and a Facebook page, as well as a video on Youtube.

Unfortunately, sometimes the best solution is to just get rid of your old monitor system and replace it. If that is the path you choose, we'd be happy to talk to you.

Best of luck,
Chris Ferro
Electrosense

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