I have to rise one more level - above the cockpit sole - before the exit(the gooseneck rise aft of the cockpit well). That last rise before exit has proven itself to be fool proof in years of following seas that have never back flooded.

So I have to contain the volume of water left in the exhaust hose - from muffler to high loop aft - at shut down. For that reason I've gone with a larger capacity muffler. I see no way I can get around that - anyone else see a different solution?

On eliminating a riser on the Red line(which I would love to eliminate!):

1-That puts the water injection point too close to engine manifold(potential splash back-corrosive gases - into exhaust port/valves).
2- Not a sufficient distance and drop to safely cool the exhaust before entering the muffler(fiberglass).
3- The injection point is not high enough above the waterline for a margin of safety.

And on the vented loop (green line) for the raw water; I could Tee that into a cockpit drain hose. One caution I have is I have had those drains clog with mussels. A rare nuisance that you clear out (with a fresh water hose blast at the docks), but if the raw water backs up in the cockpit you'd have to take care of it immediately.

I was thinking I might want to raise that vented loop above the cockpit sole for a better margin of safety. I have a few options to mount it inside a locker in the galley for easy maintenance?