Holding tanks

[Biobug]

we just purchased a 2013 Dutchmen Denali 287re. The control panel shows there is 2 gray tanks yet there is no dump valve for a second tank. I decided to let the gray tank 1 fill completely to see if it begins to fill tank 2. As I expected,it started to back up into the shower. I read that some do have 2 gray tanks as the panel shows.
Why would Dutchmen (Thor) put a panel with 2 gray tanks in a unit that only has one? I have looked everywhere for the valve for tank 2 with no luck.

[Old-Biscuit]

While use a panel that indicates 2 grey tanks when only one is installed.....

Because it is CHEAPER to use One Panel for all models

CHEAP/Less Inventory

[Campinfan]

Just because there is a switch, does not mean there is another tank. My non existent 2nd galley tank shows empty when I use the buttons.

[valhalla360]

It's not uncommon on longer units. If the kitchen is at the back and the bathroom is at the front, the plumbing to run to one tank is a hassle. Plus, you generally fill more of the gray tank than black tank if you are on a water only site.

But based on the below, you only have 1 gray tank:
https://library.rvusa.com/brochure/denaliliterature112rev313web.pdf

You might try a second experiment. Run the kitchen sink to see if the other tank fills per the panel reading.

Most likely, they use the same control panel for all their models. Our non-slide toy hauler has a position (no switch) listed as "slide out" on the panel.

[ReneeG]

We have two gray tanks: the bathroom sink and shower are one and the kitchen sink is the second, but we also have two dump valves.

[JRscooby]

With water in shower, run some in the other sink. If the level in shower does not rise immediately, start at that sink, and listen to drain water flow. Best not to need to find a full tank to use the sink

[TurnThePage]

I think that 2 gray tanks is often due to plumbing requirements, like the bathroom and kitchen being located far apart. Is that the case for you? I wouldn't be surprised at all to see an incorrect panel installed in an RV either.