Pump for fish box?

My '91 V-20 has a fish box in the floor located between the seats. It had some type of pump at one time but was removed when I bought the boat. I currently use it for storage but would like to use it for fish. Does anyone know what type of pump would have been used. My boat guy says I need a macerator pump but the drain hose is too small. Would a bilge pump work if I put some type of strainer over the drain to stop scales, etc. ? There is a switch on the dash for this pump and the discharge is located next to the bilge discharge. I tried an baitwell type pump but it would not pump when the water level in the fish box got lower than the pump. Thanks, Barry