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Old 06-28-2012, 05:07 AM   #1
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holding tank sensors

I think my sensors are giving the wrong indication. Could rust on the connections be the cause? Can the sensors be replaced? It doesn't look like they come out.

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Old 06-28-2012, 01:13 PM   #2
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More than likely they just have toilet paper or stuff stuck on them. Is this for the black or gray tank? Both can get stuff on them, food residue, etc. If it's the black, I would flush it real good with an RV toilet wand, and also you can fill up the toilet bowl to the very top (pull up on the foot pedal or pull on your white water lever, depending) and flush it a few times to help spray water around.

Then finally, the best method to cleaning that I've heard of, though I haven't had mine dirty enough to need this before, is to fill it up with about a 1/3 of a tank of water and dump a few buckets of ice cubes down the toilet. Then go pull the trailer around for a few miles, like 10-15 miles on some curvy back roads. Those ice cubes will slosh around real good and clean out the junk in the tank. Then plan to go to a dump station, dump the tank(s), and see if it's all good. Just after the drive, you should notice the indicators reading at least not full and maybe not 2/3 anymore.

This is a very common issue, so you aren't alone.

I think you can replace the sensors, but I've never once heard of it being done.

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Old 06-28-2012, 02:16 PM   #3
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Probes are Low Tech

I had a wiring problem a couple of years ago and had to pull a probe out to change the broken wire. I was able to re-insert the probe and only replaced the wire.

The factory probes are nothing more than a "bolt" albeit with a thin, round, smooth head. The head is smaller than the hole and seals with a rubber grommet. I had to really pull and wiggle to get the probe out in the first place because the nut was rusted on and the probe/"bolt" just free wheeled with the nut. Once I had it out, it was easy to remove the rusty nut and obvious how the rubber grommet would get squeezed against the inside of the tank when the nut is tightened. The loose probe with the unsquished grommet was really easy to stick back in and I used a couple of extra jam nuts so I could tighten and again seal it with the compressed grommet. There is no way you can tighten the probe without jam nuts so make sure you have a supply--can't remember the size, but they're small and thinner than a wrench which is a real pain. Once I saw the big picture, of course I kicked myself for not using jam nuts to loosen the probe in the first place.

My problem was that the wire was between the first nut and the probe. A second nut was used just to jam the first. When I re-assembled everything, I put the wire between the two nuts. These 20 something gauge wires are notorious for breaking at the probe and I won't have to remove that probe again.

Jon's advice is right on and here are a couple of other helpful links, one if you want to spend money:

Holding Tank

RV Holding Tank Sensors - Get accurate grey and black holding tank monitor readings

Probes work by having a very small current conduct through the water between a common probe and the low, medium and high. The probes appear to be somewhat randomly inserted which may account for one part of the tank "filling" faster than another. There is nothing mechanical on a probe than can break except the wire. The one I pulled out would have been maybe 5 years old and the head was still clean and shiny.

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Old 06-28-2012, 04:16 PM   #4
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Thanks all for the great info. it looks like i somethings to check.
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Old 07-02-2012, 06:57 PM   #5
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There is a product that will correct the gunk shorting out your probes.

See the lower right corner of this web page for Extreme Cleaner.
Happy Camper - Odorless Holding Tank Treatment Black and Grey Water

I bought a can of it to clean the scum off the top of the gray tank as I bought a used camper. At a M & G a few years ago Trailblazer has his new to him 5er with black tank sensor problems. We where yak'ing about it and I said, here try this. We where on full hook up so dropped in 2 scoops, filled the black tank full and went to bed. Come morning the sensors already started to work. He dumped the tank and has now started using the regular Happy Campers product.

I find that keeping your tank clean is the key to keeping the sensors working. I added internal tank sprayers and the combo of a clean flush every camping trip plus using the Happy Camper or SeaZyme tank treatment product eats off scum and paper off the probes. I have never yet had a probe miss read in the black tank since 2003 so the process seems to be working.

I did have a probe read wrong in the fresh tank. It said it was full when the tank was dry. This turned out to be a wiring short where the wire goes up through the floor of the camper, it was grounding out some how against the main frame rail.

Hope this helps

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Old 07-03-2012, 03:11 AM   #6
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Thanks John. I will try some of this stuff. The cleaners I am using do not seem to be working.
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Old 07-03-2012, 06:34 PM   #7
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A real good cleaning will help get them working again.


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