Problem with 2017 Northern Lite 9-6Q SE gray water

[Debo262]

We purchased this unit new in the fall, which was winterized. This summer, after a couple of successful trips and uneventful dumps of both gray/black water, the next time we went to empty just the gray tank nothing came out each time we opened the gray water valve. At this point, the monitor indicated that the tank was about 3/4 full (seemed accurate for what we had used), but only a few ounces came out. Back to the dealer we went, only to have them open the valve exactly as I had been doing, which now seemed to work just fine.

Fast forward to arriving home from the dealer, and I attempted to briefly open the valve, but nothing came out. Thinking that it might have something to do with being on a slight incline at the dealer (the back end was a teensy bit lower than the front), I pulled the truck from its level concrete pad to a sloped incline (rear end much lower than the front) and then opened the gray valve. A fair amount of water then emptied out, but not nearly enough compared to how much should have been in the tank. Both times that we had dumped previously, there was a definite incline downward toward the rear of the vehicle.

I then decided to inspect the valve (Bristol 1.5”) and was able to remove it, expecting to be flooded with water when I pulled it out. There was, however, NO water on the other side of the valve. The valve itself appeared to be functioning properly. I am perplexed as to why no water would have been in the pipe between the tank and the valve, and I even ran the faucet for awhile afterward so there would be some water to empty. Perhaps I just don’t understand how it is SUPPOSED to work. Can anyone enlighten me, please?

Possibly related is a missing cap from the vent on the roof above the kitchen area. There is a 2nd and 3rd vent (both still with caps) above the bathroom, presumably one for black and one for gray. Could this vent have gotten clogged somehow (debris, critters, nests) and be preventing us from emptying the gray tank? Since there still appears to be a functioning vent with cap for gray water from the bathroom, this option does not make sense to me.

I would appreciate any wisdom from the group on this baffling situation, please and thank you!

Deb Hurlbut
Evergreen, CO
2017 Ford F-250 4 x 4 Super Cab long bed
2017 Northern Lite 9-6Q SE

[BFlinn181]

If you can open the gate valve, I'd use a snake and push it up the pipe into the tank. When the tanks are installed, the builders sometimes drill the openings for fittings allowing the disk they cut out just drop into the tank. These disks can block drain pipes if they land in the wrong place. Pushing a snake into the drain line should indicate if this is the problem or not. While you have the plumbing snake, you could also drop it down the uncapped roof vent to be sure that line is open.

[Mr_Fixit]

First of all, no this is not normal. No, a blocked roof vent will not stop the gray water from draining. It might drain more slowly, but it will drain. It could conceivably suck a trap dry, but that is not likely, but it will drain.

As already suggested, it is not uncommon for trash to be allowed to drop into the tank when the openings for the fitting are drilled and my guess would be you have debris which moves around when the tank is holding water.
If that is the case, there is no good way to remove it without cutting into the tank and if the debris is larger than the tank outlet the problem will recur.

Put enough water in the tank so you are sure it should drain (I went on a service call one time where the owner was sure there was a problem and there was almost nothing in the tank to drain). Then if it doesn't drain, again as suggested already, run a tape up through the valve, you can't hurt anything doing that. If you are lucky, maybe the debris is comprised of multiple small pieces and might break free. That would give you bath in gray water, but a working gray water valve.

Otherwise, if the problem persists you will have to access the tank and replace it or cut an access opening into it and then seal the opening (no good options here).