ATF: Prowler - Gray water

Our 2012 Prowler Shadow has 2 gray water tanks. We took it out on the maiden voyage this weekend and thought it interesting that one of the gray water tanks was nearly full and the other had just a very,very little in it. We had washed dishes as well as taken showers so felt there would be gray water in both tanks.
We were thinking when we bought the camper that the two gray water tanks were like our old travel trailer. The old camper had a gray water tank for the galley and a separate gray water tank for the bath room. Now, we are wondering if the 2nd gray tank is an overflow tank for the 1st tank and since we hadn't filled the 1st tank, the second tank had just a little bit that may have sloshed in it while driving to the dump station. Are we correct that the 2nd gray tank is an overflow that only fills if the 1st tank gets full?
Thanks for your assistance and by the way....we love the new Prowler....next trip is a 10 day stay in two weeks from now.

I am not sure about the Prowler but every other model has a gray tank for the galley and a gray tank for the bathroom. A black tank for the toilet. To check the plumbing I would be sure they are both empty and then fill them one at a time to see how it goes.