Bilge Pump Non-Return Valve

[Dockhead]

I installed a couple of Rule 4000 bilge pumps last year in my boat to supplement the ones the boat came with. The installation was fairly involved since these big pumps need big hoses and their own through-hulls.

The manual says under no circumstances to install a non-return valve in the line.

But when these pumps come on automatically (Ultra Junior float switches), the large diameter hose retains a lot of water. When the pump switches off, this water goes back into the bilge. Then the pump switches back on. And so forth.

I am no longer on shore power and I'm worried that this endless loop might drain my batteries when I am not on board.

What to do, other than install a non-return valve??!!