Late last season I had the pleasure of a sailing guest aboard the boat leave the head pump valve lever in the wet flush position and not in the dry bowl closed position - after having received careful instruction on using the head before leaving for Block Island. The end result was 18 gallons of sea water in the holding tank and the head overflowing into the bilge with no way to pump out the holding tank as the boat was only set up for deck pump out. Nothing like bringing 18 gallons of Block Island sea water back across Block island Sound to be pumped out back in Groton, CT. With the head installed below the waterline it is so easy to see how boats can be sunk!
Last summer I had asked members on this site for some installation options as I'd been considering installing a manual pump out option ready for some long distance cruising
http://www.ericsonyachts.org/infoex...-Plumbing-Need-Ideas!&highlight=HOLDING+TANKS
So this winter I decided to kill two birds with one stone so to speak. Install a manual whale pump and an anti-siphon loop. From the Ericson 38 systems blueprint there was a factory option to have a 2nd hose from the holding tank to a manual whale pump behind the head and then to the 1 1/2" thru hole under the head basin. My boat already had the cut out hole behind the head and the 1 1/2" sea-cock ready for this installation. A long "shitty" story short I have installed a Whale Mark V Sanitation Pump with 1 1/2" Raritan Flex Sanitation hose, trust me trident hose is just too darn stiff for the bends required for this installation. It required me having to take the Whale Mark V pump back cover off (this a feature of the pump) so I could align the in/out ports on a 45 degree angle to manage the bend of the sanitation hoses in the little space behind the head cabinet. I can't say that I enjoyed this job as it was very hard work.
There is not enough room behind the cabinets for an anti-siphon loop for the sanitation hose but I did manage to loop it high enough behind and under the sink to be just above a non heeled waterline level. In addition as the manual pump out sea-cock will at all times be sealed closed (per USCG no discharge regulations) and only used when I'm actually pumping out I don't see the lack of an anti-siphon loop as big deal.
https://www.defender.com/product3.jsp?path=-1|51|2234226|2234230&id=152824
https://search.defender.com/?expression=raritan+Hos035A
The next job was addressing the big issue of having the head available to be used without having to open and close the head sea-cock every time you want to use it. For this installation I installed a Raritan vented anti-siphon loop in the cabinet above the head and ran 3/4" Trident hose from the head pump to the anti-siphon loop and back to the head and about as high up above the waterline as practicable in an Ericson 38 head cabinet. This required drilling some holes through the cabinet panel. I'll be honest I won't be able to test this loop until we splash in a few months and it may also require a small length of hose to be added to the end of the vent and snaked up higher in the cabinet.