[jrd22]

Thanks for all the replies, it makes sense to have it on the pressure side of the pump going to the bowl. Calder's book just shows it between the thru hull and head, it wouldn't work that way. The top of the bowl is above water line, except when heeled over on stb. tack so I'll put one in. I also need to install one on the discharge hose from the holding tank that goes to the macerator and then to the thru hull (the same thru hull used for the direct overboard discharge, there is a SS manifold on the thru hull). This line runs horizontally just barely above waterline and would be under water when heeled allowing water to run back through the pump and into the holding tank if the Y-valve is open to tank.

Thanks again, John