I can't speak to your floor structure, Bill, but no doubt others here are more familiar with it.
As to connecting the lines, as apparently Harry has done, I think the only negative aspect is that the vacuum break is there for a reason - to help prevent contamination from backflow of hose, fittings, etc., but mostly the water source. To my notion this is very unlikely, but then again that's why backflow devices of many types are available for protecting various water resources, public and private.
I would be careful flushing though, and use a pressure regulator on the hose... I keep one on my separate flush hose. You don't want to blow off your spray heads into the tank... they are sensitive to that possibility.
I think mine is not in perfect shape either, since some water backs out of the water bay connection when I remove the hose... it didn't used to do that. But I use a separate hose especially for the flush function, and rinse it for a few seconds before draining and storing it. I think as long as you use common sense efforts to counter any possibility of contaminating anything, you should be good until you can replace the valve.
The Sani-Flush system, when used regularly, is a great way to keep sensors from fouling and dump valves from jamming, etc. The gray tank, Harry, gets kitchen detergents, other soaps, and perhaps even laundry detergents. It's going to be by nature "cleaner" than the black tank. At least the gray tank will naturally suspend and flush solids much better than the black, so only the addition of the occasional tank treatment might prove helpful. I often pour Thetford enzyme formula in the traps if they sit unused for awhile. But each owner has their own preferences.
Joel