Mine is an early mark 2 and has an after-market plastic holding tank under the port side bunk, forward cabin. This is as close to the head as you can get with minimum piping. 3 way valve under the forward sole for choice of tank or o/board discharge; pipe in bulkhead / hull corner to deck pump out point; and anti siphon loop adjacent to that on hull side. The tank must have been made from templates but no makers info on this 2nd hand boat. It all works well including electric ‘Full’ indicator light, photos of you want when I get on the boat again.