Cross Tank Dumping and Horst Probes

[Herk7769]

Well, I learned another new thing this week.

I have Horst Probes in my black water tank and my gray water tank.
Anyone who has them knows they work GREAT.
http://www.forestriverforums.com/for...ion-16089.html

Suddenly my gray tank stopped indicating properly and I was devastated to say the least. It indicated full when empty; after cleaning 1/3; after a second cleaning 2/3; I was going crazy.

I tried everything with no consistent results.

Yesterday I removed the gray tank probes and found TP bits wrapped around the coil of the gray water probes. HEAD SLAP! IDIOT!

Following the advice of a previous thread about NASCAR campers who added an end of mast shutoff valve to allow transfer of gray water to the black tank to extend stay times while boondocking, I tested it this summer and it worked as advertised. I was very happy.

Till this happened. HOW it happened I have no idea because the water should have flowed only from the gray tank into the black with mixing only in the black tank. That was the theory anyway. Most likely works fine with the button style probes; but the Horst "coil type" probe is unforgiving of solids and paper as it gets trapped in the coil spring and is very hard to clean.

Everything is back working correctly now; but what a learning experience!
If you will be using this "transfer" method and install the horst probes, use the black tank type in both; just in case.

[SaskCampers]

Good catch Lou, must have drove you nuts knowing how thorough you are.

[Fire Instructor]

Having successfully used the gray to black transfer method for a number of years, and it may have been one of my posts where saw the idea, I'm struggling to figure out how TP could have back-flowed into the gray tank....

If the gray is near-full, a standard rule of hydraulics is that fluids seek their own level. As long as the black tank has a lower fluid level than the gray, water should only flow in one direction. The only thing that I can think of is that when dumping, if you dump both simultaneously, and both tanks are at near equal capacity, I suppose that the hydraulics of pipe diameter might allow this to happen.

I use the three valve method all the time, one on gray, one on black, one at the discharge (allowing me to transfer), but at no time (except when draining the last few dribbles following the pre-winter cleaning), are all three open at the same time.

[Herk7769]

Originally Posted by Fire Instructor

Having successfully used the gray to black transfer method for a number of years, and it may have been one of my posts where saw the idea, I'm struggling to figure out how TP could have back-flowed into the gray tank....

I am with you dude. The only thing I can think of is that the water "glugged"; sucking black water into the sewer tube and the back and forth glugging as the gray water flowed into the black tank allowed some crud into the gray tank.

Just saying what I found; and am no hydraulics expert.
The procedure I used was:

1) ALL Valves Closed
2) Open Gray water valve and charge sewer pipe (end valve closed).
3) Open black water tank allowing gray water to flow into black tank.
4) Closed black water valve
5) Close gray water valve

Somehow black water still wound up getting mixed with the gray water in the gray tank. NO idea how it happened.