A word of caution on that second black tank valve. I learned this the hard and very stinky way. We have one on our Axis 25.5. No one told us about it when we did our delivery walkthru either. Mistakenly, when dumping, I'd open the "hidden" valve, then go to the wet bay to dump first the black, then gray tanks. Pulling that hidden valve put a lot of strain and pressure on our plumbing pipes and I learned, again, the hard way, that Thor doesn't put a lot of cement on those plastic plumbing pipe joints. So, on a trip in GA, I pulled the valve, preparing to dump. That's when the black water pipe separated, just behind the wet bay. What a horrible, stinky, nasty mess! And, of course, our black tank was full. We headed straight home after that and I totally rebuilt our black water system, using high strength cement and wrapping the joints with self-bonding plumbing tape. Now, when dumping, I open the wet bay black valve first, then pull the 'hidden' black valve. That way, the sewage runs straight to the stinky slinky hose and down the dump station drain.
Be careful out there!