First: Welcome to the Forum!
I had two black tank valves in my Outlaw.
I always opened the one on the passenger side last, and closed it first...
This gave "last night's dinner" a running head start toward the drain on the driver's side of the RV. I closed it first so that there (in theory) would be nothing left in the cross-pipe when I was done.
(The gray tank valve got handled just like any other gray tank valve... nothing special about it)
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