recently when our dump outlet on our heads (two of the four) blocked up, we had a real problem but discovered a handy trick on the Lagoon 450 black water tanks that probably works for a few different boats.

The pump out hose and fitting on the deck aligns directly with the dump out pipe from the bottom of the black water tank. So with a little jiggling you can run a hose from the top all the way through the black water tank and out the bottom past the dump valve (thruhull).

This means if you have a severe blockage , as we did, you can use your Deckwash and under pressure blast your way through the blockage, as you would with a household blocked pipe.

We combined this with some Muriatic acid (neutralised with baking soda) to get us moving again.

A good trick if just a small blockage is, with all valves open, insert the deckwash hose down into the top of the black tank, via the pump out, using both the water pressure and pipe pressure as a clearing tool to release the blockage.