Phill is right, test the pump with the correct polarity(battery positive on the red marked side) on a 4.8 volt battery and check flow direction, these pumps are designed to run in one direction, running them in reverse will not be efficient, the gears are designed to seal the suction in one direction.

if you look at it from the tubing connector side, with the connectors to the bottom (below the centerline) the right side connector is the suction side(the line with the filter is on the "output to turbine side")...