Yep, that is where our set up differs. I never pump directly overboard
anyway and the pump will be used infrequently. Like most NE mooring
fields we have municipal pump out service
that comes around for free; raise the pump out burgee when you leave and like magic the tank is empty when you return.
So I have been thinking of your set-up and the conflicting info from SeaLand. If you look at the diagram and read #3 they are in direct conflict with their own instructions. Have you spoken to them about this?