IF..... there is a T in the exit line fitting at the tank and you can open a small valve and empty it into the bilge, that will work, but is rarely found.
I use a small centrifugal pump with a 6' discharge hose, dropped into out 38 gal. tank thru a clean-out port and rapidly move 90% of the water over to the galley sink.
Why? To save unwanted wear on the $200. + electric fresh water pressure pump.
Is the present tank stock? Any access via a clean-out port?