MSD replacement

[Les Murray]

Peggy,I am planning to install a new head this winter and have a general question on the plumbing. The current arrangement in my head is I have a 1/2" OD hose comming from the thru-hull to the pump on the head, then connects to the head itself. There is no vented loop anywhere in this connection. The head generally above the waterline except on starboard tack. The exhaust line is 1 1/2" hose exiting the MSD, through a vented loop, and to the holding tank, via a Y valve (for pumping overboard).My question is where are the vented loops necessary or advised? Does the vented loop between the head and holding tank make sense? From a previous post on this site, it seems to be good insurance.BTW, the current head is a 15 year old Grocco HE. I am replacing it with a Raritan PHII.Thanks for the input.Les Murrays/v Ceilidh'86 C-36 #560

 

[Peggie Hall/Head Mistress]

Install a vented loop

in the head intake--which is actually 3/4" hose btw...it goes between the pump and the bowl. It's your best insurance in case the thru-hull is left open and/or the dry/flush valve is left in the wet position...I've been aboard boats on which the toilet has overflowed less than half an hour after leaving the dock 'cuz we stayed heeled on the same tack. As for whether you need one in the head discharge: if you spec the inlet and vent fittings on the new tank away from the hull, toward the centerline--so that when you're heeled tank contents flow away from the fittings on one tack and the hose runs uphill on the other tack, you won't need a vented loop. But if the fittings locations allow heeling to send waste into the hoses, put it in.