Head Is Siphoning . . . Not Mine, My Boat's

[sailstoo]

I rebuilt my olde Wilcox Crittendon head (yeah I know, I shoulda just put a new Raritan in but I found a rebuild kit cheap) and it now has an "annoying" habit. If the select lever (pump out waste/pump in water) is left in the pump in water position after a couple pumps, and not switched back to the pump out bowl position, water just keeps siphoning in. This is not a reassuring situation as we occasionally have "new to marine heads" folks on board. So, what'd I do wrong or is this just something the olde Wil-Crit heads do? Is there some sort of anti-siphoning valve I can put on the hose between the through hull and the head? As always, thanks in advance.

[peghall]

You need a vented loop in the intake. It needs to be installed between the pump and the bowl, NOT in the line between the thru-hull and the pump...and it needs to be at least 6-8" above waterline AT ANY ANGLE OF HEEL, which on most sailboats puts it 2-3 FEET above the bowl.

Unfortunately, Thetford didn't see any need to mention that in their installation instructions, but fortunately every other manual toilet instructions do and even include a drawing showing where it goes. Here's the manual for the PH II...see illustration 1A on page 5: http://www.raritaneng.com/pdf_files/ph_II/L04v0505.pdf

When you buy the loop (3/4" btw) be sure to buy the air valve for it too. You may have order it separately. It's a one way valve that only allows air INTO a line to break a siphon, nothing out...it threads into the nipple at the top of the loop. Do not put a vent line on it instead, 'cuz it's so small that it'll very quickly become clogged with salts and minerals, turning your vented loop into an UNvented loop that no longer has any ability to break a siphon.

[sailstoo]

Thank you Peg. I have now ordered your book from Amazon.