John - you still need a pump of some sort between the below the waterline thru hull and the tank. Maybe you assumed that was obvious. But you are correct, if there is no direct head to overboard path, you don't need the anti-siphon loop on the discharge side. Some say you need it on the intake side, but if you are using a fresh water flush method (basin drain connection) you do not need that either.
Yes, I assumed the manual plastic whale pump in between as you said, but I should have called it out. And correct also that the holding tank is lower. And I am using freshwater flush.
Absolutely great to hear I don't need it as the room in a 25 for plumbing is very tight. You guys are tight on 30+ footers, imagine running it in the 25.
Thanks for the reply!