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tkcas01's avatar
tkcas01
Explorer
Aug 06, 2013

After 7 years of full timing, holding tank sensors now WORK!

I bought this rig in 2005 - a year old from the original owner. As many have experienced, the holding tank sensors have never really been reliable - the black tank sensors worse than the grey tank.

If you search my posts, you will not find a shortage of my posts telling other posters to give up on the hope of the holding tank sensors working properly. Well, hopefully it is only crow I need to eat, as my tank sensors are now working perfectly! There is hope! How did that happen, you ask?

Let me start by describing my typical holding tank protocol over the years. I immediately started using the rig for full-timing. I would typically stay in one location for several weeks or months. As one would expect, I would leave the black tank closed until it needed dumping. Since the sensors were pretty unreliable, I could tell from the way the toilet flushed when it was getting full.

The grey tank I would typically leave open (especially since I use the washer/dryer alot), until I felt it was getting close to time to dump the black tank. I would then dump the black tank, use the factory-installed tank flush system to flush it, then dump the grey tank which would "clean" the stinky slinky. Mind you, the tank sensors remained unreliable. One other important point - in preparation to leave a location, I would always dump so I would be traveling without the added weight in my holding tanks. One other unfortunate note - in the last year or so, the factory-installed black tank flush system has clogged and no longer works.

Then earlier this year, I was in a situation where I was parked for 4 months and needed to use a macerator to dump. I had bought the Flo-Jet system. I followed the recommendation to dump the black tank, then shut off the macerator and open the grey tank valve to let the grey water back flush into the black tank. The macerator also has a water hose connection on it so you can back flush with fresh water, which I did a few times during my stay there.

With all this, I started to notice the sensors on my tanks behaving differently, but still not perfectly. When I left this location where I needed the macerator, I stayed for a week at a State Park where I had no sewer. While there, my holding tanks of course started to fill. Rather than dumping as I left, I decided to let the contents slosh around during my 400 mile journey to my next stop. I didn't add any ice cubes or Calgon as you might read about in other posts. Just drove.

I hope this is not too much information (TMI), but when I arrived at my destination and dumped, through the clear sewer connection I have I could see that the contents of the black tank had been thoroughly "blended". As it drained, there was not a sign of any solids - TP or otherwise. I was also surprised at the "solids" that came out of the grey tank - some black and some white. Clearly alot of buildup of soap scum, kitchen matter and such in the grey tank over the years.

Since I no longer needed the macerator but like the back-flush idea, I purchased the Flush King that would enable me to continue using the grey tank contents to back flush the black tank. After just a few dumps and back-flushes, the sensors were clearly behaving differently. Still, the black tank was not showing empty after dumping. Referring to the manual, I removed the instrument panel and used a screwdriver to calibrate the LED readout so that it read empty after I dumped.

Now when I dump and back-flush (using the grey tank only - not using fresh water to back-flush either tank), the indicator lights magically go to EMPTY. And as the tank fills, they magically indicate the increased level. Suffice it to say that I had long ago given up on factory holding tank sensors as a joke that would never work. I just happened upon a sequence of events that proved just the opposite. I'm disappointed that my factory-intalled black tank flush system is inop, but it seems that this back-flush method, possibly combined with a drive-and-slosh strategy might just be the answer.

I hope this is helpful to others. Happy Dumping!
  • "Referring to the manual, I removed the instrument panel and used a screwdriver to calibrate the LED readout so that it read empty after I dumped"
    What manual and what panel????
  • tandkj wrote:
    "Referring to the manual, I removed the instrument panel and used a screwdriver to calibrate the LED readout so that it read empty after I dumped"
    What manual and what panel????

    Good point. Since I first battled this years ago, not sure where I learned what I know! But to help, here is my indicator panel...



    And in my quest to help my fellow RVers, I removed said panel and here is the backside...



    If I remove the little circuit board, on the back side of it there are a couple of adjustment screws for the sensitivity on the holding tanks...



    So after I felt I had both my holding tanks thoroughly flushed and empty, I used the adjustment screws to have them register empty - just a slight turn off of showing an indication of 1/3 a tank. Seems to be working for me.

    Hope this helps.
  • my sensors work great after 7.5 years... I just keep the black tank clean with a wand and if the grey starts acting up, I run some of that TST lemon clean thru it.
  • Great report. The in tank flusher is easy enough to clean if you can get to it of course. Many have drilled the tiny holes out. I had to replace mine after it actually broke.
  • I used the Flush King for years on our old trailer with great results. Our new trailer has a built in sprayer in the black tank. I'm not convinced the sprayer gets the tank anywheres near as clean as the flush king. Im planning on using both for our new trailer. Might get a hydro flush and separate valve which would accomplish the same thing and is a bit cheaper.
  • I had one of my factory black tank flushers clog. It was after my wife spent 2 months in it recovering from knee surgery... A long story as to why for another time and place.
    I drilled it out and no problems since.
    My sensors have always worked well for us in several TTs. But normal use for us is driving home at least 120 miles, and several miles of rugged dirt roads when leaving camp.

    As you experienced, I see no solids to speak of when dumping. I am of the belief that many always dump at the campground, and solids don't get dissolved, and end up accumulating in the tank.

    The campground dump station may be real convenient, but it may well be a source of tank/sensor problems.
  • Huntindog wrote:

    The campground dump station may be real convenient, but it may well be a source of tank/sensor problems.


    Agreed, I usually take my black tank with me to my new location, gives it some time on the road to... bounce around.. then at my new location with my first grey tank dump, I get the black tank. Have built in flushers, not sure they do much really.

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