David,

I wouldn't rely too much on the owners manual, typically, their not
very detailed. And most boats have all kinds of extras installed by
yards or the owners after the fact. But I guess it can't hurt to ask,
try the manufacturer. You will probably be better off taking the
screens to a good marine supply store, they may have them in stock, if
not it's back to the manufacturer. Every vacuflush I've seen runs on
fresh water, try filling the water tank, but I guess it could run on
sea water, so the boat will need to be in the water if that's the case.
Keep a long thin screwdriver handy, those toilets do clog, just clear
the hole in the center to unclog the unit. Being as your new to
boating, try to avoid the, "deer in the headlights" look on your face
when you head to a yard for work, they can smell blood in the water
better than any shark ever could.

John