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Holding tank in 33 Mk2

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    Roger Sturge

    My 33 MK 2 doesn’t have a holding tank. Is anyone able to advise me on design, siting within the boat and whether ready made equipment is available?

    Alasdair Woodfield

    Hi Roger,

    My recommendation is to go for a plastic tank, not the stainless steel as used in my 2006 331.

    I have this summer had to pull the tank out for some welding on one of the hose spigots, crevice corrosion. Siltala apply an adhesive where the hose is clamped and that together with ‘poo’ sticking on the inside leads to corrosion. The hoses are a ‘pig’ to remove because of the adhesive !

    There are plastic tank manufacturers, e.g. TekTanks, who will make, (at high cost), you a tank to fit a suitable space using dimensions you supply. Whatever you choose to do ensure you have an access hatch fitted to clean the tank out.

    Good luck with your project.


    Alasdair Woodfield


    One other consideration, make sure your installation has the vent and the fill hoses routed such that tank contents cannot lie in them. In the 331 the vent hose has a downward routing, not good !!



    Hi Roger,
    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.

    Ned Coackley

    Roger Sturge

    Thanks Ned

    The port hand locker in the forecabin of Wild Cat (1977 mk2 33) is obstructed by the ducting from the air heater and to a lesser extent by the wiring to the mains socket.

    I wonder if anyone has experience of fitting the holding tank in an alternative position. The alterntive sites seem to be the the cupboards behind the head or possibly further forward in the forecabin. The letter would have the benefit of siting the pump out access well forward of the water filler.

    Where is it placed in those 33s that had a holding tank as original equipment?


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