Chris,
I am not an expert on the P235 but I do have professional expertise in marine sea toilets.
Three points:
Firstly, ball valves per se are fine, but you should make sure that you only use marine grade brass DZR CW602N (CZ132). This is easier said than done, as many chandlers just stock the cheaper, ordinary domestic grade ones which look outwardly identical.
Every volume production boatbuilder uses brass Ball Valves, screwed to Through Hull fittings installed from outside the hull rather than traditional seacocks which are installed from inside the hull. The sole reason that they do so is cost, and the reason for the cost difference is almost entirely in the raw material. You may well be able to source marine grade bronze or gunmetal Through Hull fittings, but not so Ball Valves. Do not economise by buying anything less than DZR [DeZincification Resistant] ball Valves & Skin Fittings - for a succinct explanation and the correct standard to use, follow this link:
http://www.aquafax.co.uk...s/aceimages/TechData.pdf Secondly, whatever you do, don't even think of using brass screw down gate valves, even on the inlet - sooner or later dezincification will occur and the spindle will break off inside the valve.
Thirdly, to minimise the risk of sucking in what you have just pumped out, the intake should always be well forward of, and higher than, the outlet; ideally each should be on opposite sides of the boat. If you want to be able to use the toilet whilst sailing, ensure that the intake is below the heeled waterline.
sincerely
Geoff Sheddick
Parker 27/146 "Stroller'
Geoff Sheddick
Parker 27/146 "Stroller'