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Keith727 09-18-2009 07:56 AM

Black Tank filling from fresh water tank while traveling.
While driving water from the fresh water tank fills the black tank..has anyone experienced this problem before??

2005 DSDP 3815

Thanks, Keith:banghead:

Luv2go 09-18-2009 08:18 AM


My first thought would be that your toilet was leaking, but it would take both the fresh water valve and the flush valve to do that. In our old coach, the bathroom sink was plumbed to the black tank, but that was a Gulfstream and I don't think Newmar does that (at least they didn't in our coach).

Do you have your water pump on while this is happening? If so you could turn it off and see if it still happens, that may give you some clues as to where the leak is.

Good luck!

read & learn 09-18-2009 08:23 AM

Are both of the holding tanks empty when this happens. If not are you sure the dump values are closed.
Is the water pump off.
It is hard to understand how water could get passed the closed toilet value.

Keith727 09-18-2009 08:59 AM

All valves are closed....Pump is off.. The Black tank was empty...Fresh water was only about 1/4 full...I don't see how it siphones from the fresh water tank, but I guess it does...This has happened two times....

DandS 09-18-2009 09:34 AM

Hi Knot-flyin, welcome to the forum. There should only be one direct connection between the fresh tank and the black tank and that would be the toilet water supply. Would suspect a leak in that system somewhere if what you describe is happening. Can't imagine any other scenario where you would go from fresh to black - a connection like that could be an ugly mess. !! :sad:

Luv2go 09-18-2009 09:45 AM

You don't happen to have the blackwater flush somehow hooked to the freshwater tank? It's a long shot, because they have vacuum breakers that would keep a siphon from occurring.

Another thought, it only happens while driving, that means agitation in the freshwater tank must be pushing the water into the black tank somehow, maybe that is how it gets past the vacuum breaker.

I agree with DandS, whatever it is does not sound good...

"007" 09-18-2009 01:03 PM

If you have two baths the smaller bath sink empties into the black tank for that toilet. If you over fill your fresh water tank the water will siphon out of fresh water tank while driving.

Keith727 09-19-2009 07:40 AM

The DSDP 3815 has only one bath..The black tank flush has no valve that I'am aware of. Just hook the hose up and turn water on. There is a valve you turn on to fill fresh water tank. The hook up for the fresh water is seperate hook up from the black tank flush hook up.

2005 DSDP 3815

ronmc 09-22-2009 04:40 PM

Your vacuum breaker valve could be leaking. Sealand toilet, on back of toilet.

69RoadRunner 09-23-2009 06:10 AM

Are you actually getting water into an empty black tank, or are you reading the levels on the display?

TandW 09-23-2009 07:27 AM

Any fluid remaining in tank moves around and "remakes" the high resistance connections for the tank level sensor. Think of your gas guage moving about the half mark as you manuever steeps and inclines. Good luck!!

Keith727 09-27-2009 08:05 PM

The black tank was empty and fresh water tank about 1/4 full. I drained the black water tank which had about 25 gal. in it and the fresh water was almost empty.

2005 DSDP 3815

69RoadRunner 09-27-2009 08:08 PM

I figured you had, I just wanted to be sure, because that's all I could come up with if the toilet isn't leaking.

Maybe you aren't completely draining the black tank because of a clog. Then when you drive around, that breaks the clog?

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