RV Holding Tank Indicator Not Accurate

by Dave Brimlow
()

How to Fix an Inaccurate RV 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.

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ANSWER: No you have not missed a dump valve. It sounds like your RV holding tank gauge may not be 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 the gunk on the probes. So again, do not use the Dawn in your Fresh Water Holding Tank.

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

Take a look at the video below for more suggestions on cleaning your holding tank monitor probes as well as how to prevent this from happening in the future.

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Here are links to some of the items mentioned in the video:

RV tank cleaning wand

RV toilet paper

RV Probe Cleaner

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

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Whichever soap
by: Anonymous

We had a (2nd hand) Jayco travel trailer -- Seems only a few trips and the sensors started sticking.
Instead of using Dawn and leaving it sit a while, we used 'dishwasher' detergent. About 1-2 cups and 1/2 tank of water.
When you are getting ready to leave for your next destination- drain and rinse your tanks, fill to about 1/2 with water, put in dishwasher soap, and drive to next destination. If this site doesn't have sewer, find a one close and dump.
The natural "agitation" of the drive/road helps to wash the sensors AND walls of the tank. You might be surprised at how much is stuck in there - we sure were, so Don't be afraid to do this again on your next relocation!
And as everyone else says: NOT for use in fresh water tank - only black and gray!

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RV Holding Tank Not Accurate
by: Anonymous

I’ve had three RV trailers and two M.H. and learned what has to be done and what should be done. My first RV’s were travel trailers and that is where gained the experience of researching info on this subject. First and foremost IRV2 was very helpful in suggestions. Another great web site is www.oemys-performance.com mostly dedicated to M.H.s. Keeping your black water and gray water tanks clean is a must or your playing a guessing game. I’ve had an RV of some sort since 1973 and you learn sometimes by trial and error, but a little preparation makes your trips much enjoyable.

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Tank Indicators won't read FULL
by: Anonymous

Most posts I found relate to tank indicators still reading some level despite the tanks being empty. It's relatively straightforward to understand that debris still stuck to the side of the tank (more specifically, the sensors) are likely the cause for this condition.

But what do you do when your indicators won't read full, even when the tanks are overflowing? This was my struggle and I wanted to share my solution and some discussion.

First, a disclaimer. My particular setup may not match yours and therefore the proposed solution may be different for your application. This also assumes that all your sensor wires are connected, no broken sensors or wiring problems are present. I have a Keystone Toyhauler (Raptor) with the Jenson InCommand system. There are five tanks - One 120 gallon freshwater tank and four 40 gallon holding tanks - 2 black and 2 gray.

I am maniacal about rinsing out the black tanks until completely clear. I start the built-in tank rinsers while dumping, then fill up the tanks again with the rinser and dump a second time. So my particular situation had nothing to do with debris stuck on the sensor as in the case where you have a reading with the tanks empty.

Turns out there was some buildup, but maybe not what you'd think. I had problems with BOTH the gray and black tanks not reading full. I read an article explaining that just the oils from your skin and hair, along with soap, shampoo, etc. would leave a residue on the gray sensors that would eventually prevent the sensors from reading properly. This made sense to me, so I followed the directions of dumping "gobs of Dawn Ultra" down the drain and washing it down until the tanks were full. I did this for both the gray and black tanks. By "gobs", I poured two solo cups full down the drain (I found a gallon of the dishwashing liquid normally used in restaurants on Amazon for under $15). After letting that sit for 5 days, two of my tanks read full! The other two "almost" read full (meaning they would kind of bounce between 2/3 and full).

What I learned next has to do with calibration. There's a YouTube video about tank calibration that involves turning a small screw to "set" the reading properly to a known full quantity. But the InCommand system has no such calibration. Turns out it does, but it's all electronic and buried deep in the admin menu (call InCommand support for instructions). In my case, you can vary the resistance to alter the tank readings (values range from 0 - 255K Ohms). Mine were all set to 0.

So, with all tanks empty, I filled up 5-gallon buckets of water and stopped at 10, 20, and 30 gallons. I hoped that I'd read 1/3 full at 10 gallons, 2/3 full at 20 gallons, and Full at 30 gallons, still leaving me 10 more gallons of "buffer" before the tanks overflowed. Two of the tanks did exactly that. The other two I had to calibrate slightly. In my case, one tank I set to 50K ohms to read full at 30 gallons, and the other tank required a setting of 150 K ohms to read as desired.

A couple of points. In my case, the tanks never really read correctly, even when new. This SHOULD have been done at the factory, but clearly was not in my case. Don't do this until after you've thoroughly cleaned/degreased all your tanks and you are certain they are "squeaky clean". I will now do this every couple of years as preventive maintenance.

I hope this helps others with similar situations.

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Simple System
by: Anonymous

Turn off the pump flush the toilet hold open the valve and look down into the tank.
You can see where the level is.
All of my RV's have had a straight pipe into the tank.

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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.

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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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