Grey water tank(s)

[Notanlines]

We have a new '17 38rssa. We have had a number of 5ver's, but I don't understand this. When I open the water service door I have one black water pull T and one grey water pull T. The black water empties fine and reads 0-6 or so every time I drain the tank. The grey valve pulls fine, I can see the water emptying through the clear extension, but the gauge only will go to 46. I'm not sure if this is a faulty gauge or if I seem to be missing a grey water valve somewhere. All our other RV's had one black water tank and two grey water tanks with a separate handle for each. Any help would be appreciated.