Peggie, I know you have gone over this a hundred times but I recently changed my mind about using a Y-valve in the system and now do not have the benefit of your advice when I figured this out the first time. I have a 1974 H-25 that was originally fitted with direct discharge. I am installing a small (9 gal) rigid holding tank and want to do away with the whole Y-valve. I would like to have the 1-1/2" line go from the potty to the tank and then have TWO exit lines, one to the deck pumpout fitting and one to a 1-1/2" manual Whale pump to empty the tank at sea. The tank will also have a vent line running up to the deck on the other side. (After reading your exchange about Dr Stavis's Rhodes Reliant I know to keep this line pretty straight and short; it'll be about 30 inches high and about 15-17 inches outboard of the tank.) The question is-- between what two components do I put the vented loop(s)? And should I vent them to the deck or just leave them alone? Sorry for asking a question you get about every ten minutes. JC cherubiniyachts@aol.com