I'll take your word for it, but it makes no sense to me why the fresh water pump would be labeled "Dump", and not "Pump".
I was just guessing, but I would have thought it might be something like a macerator sewage dump pump
or perhaps one of those two tank set-ups where one tank has a macerator pump that transfers to the other tank for gravity dumping.
Why not flip the switch and see what happens?
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