Black Tank design - need advice please

[Honey Ryder]

I am designing a black tank and want to make sure I haven't forgotten anything before I hand the design over to the manufacturer and wonder if the forum can add any ideas or suggestions.

I will have an black water inlet, an outlet for an air vent, an outlet for a pump-out, and outlet for a drain through-hull, and an auxiliary outlet to feed another tank. I will add one or two inspection hatches.

The tank is about 100 litres, will receive from a Blake Lavac manual toilet, and will be made of plastic (for tanks).

Does it make any difference where the pump-out outlet is situated? Presumably it should be positioned at the bottom of the tank to aid evacuation of the tank?

I have never pumped out a tank before...so what do you do...do you close off all inlets and outlets and just leave the vent open before you pump-out...or??

Thanks for your help everybody.

[Pelagic]

Some notes:
Make sure the Vent is positioned so that fumes do not get drawn back inside.
same outlet for discharge via pump and Y valve to thru hull OR pump out.

Make sure black water thru hull can easily be accessed for shut off and maintenance.
Why do you want an auxiliary tank?


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[Boatguy30]

Make it gravity drain if you can mount it above the WL. Line up the deck pumpout with the hole for the drain so you can clean it out with a stick if needed.

[Honey Ryder]

thanks for the advice.

i am mounting the black and grey water tanks above deck and taking the discharge back into the boat via through-deck mountings and they will then gravity feed through seacocks just below the waterline.

i will probably go with two vents to increase air flow, and use one of them as a pump-out.

my black tank is only about 100 litres, which is why i may add the auxiliary tank into the design.