For what is it worth, here is what I do about the fresh water overflow problem;
I have a whole house filter that attaches to the hose to the water source. A short hose goes from the filter to the boat water intake. The filter 1) makes sure that there is never any chlorine or dirt in my water tanks, and 2) slows the flow of the water coming in. I see how long it takes for the first 100 liters and then I set a kitchen timer for the amount of water I want. When the timer goes off, I turn off the hose.
I do also have a backup electric pump that I bought after a dishwasher incident. The pump is a big, heavy thing that hardware stores sell for pumping water out of flooded basements. It is centrifugal so bits of paper and debris do not bother it.
Miles s/y Ladybug, sm 216 Martinique