There are several ways to go about it, but I'd re-plumb so that you can pump your holding tank overboard
. You didn't mention if the tank is above or below the water
line. If it's above, my favorite system is to pump the head
into the holding tank
and let it gravity feed out. If you are where it's legal
to discharge overboard
, you can just leave the valve open. If not, you just close it until you are where it is legal
and appropriate. No pumping required.
If the holding tank is below the waterline, you can run it to the through hull
with your pump in that line and a y-valve to separate it from your other line. Or you can once again have everything go to the tank and then either pump it over or have it pumped out.