Plumbing and Vacuum Issues
I'm thinking about doing this too, but have some questions. Since I don't always have the thru-hull valve open when at the dock, I'd rather use a Y valve to divert the sink drain either overboard or into the head intake line. It would be a lot more convenient to connect this under the sink, rather than run another hose down to the seacock. Then to close up the system I would (a) switch the Y valve to the intake line, (b) run water into the drain (presumably pushing the sea water in the line out the seacock), (c) close the seacock, (d) run more water and flush the head out, and (e) put the Y valve back to normal. Does this sound like it would work? Now another complication. The intake line and head are all below waterline. There isn't a vented loop in the line, but I feel like I should install one. The instructions for my electric head recommend installing a solenoid valve on the vented loop to prevent air messing up the pumping action. Since the sink drain won't normally be connected to the head, it shouldn't be a source of air. But if I run sink water into the head intake line, won't it run out the vented loop, which will be lower than the sink drain? Thanks for any help. - Walt Bilofsky
