Could yo be more specific? I'm not sure I understand how "the output works" if you are not getting any suction ... what exactly are you seeing? Can you hear the impeller running when you plug it in?
Assuming that all tubing has been properly connected and that you've followed the instructions for assembling the unit, and that the pump is actually running, then it is most likely that the unit is vapor locked - a common problem with centrifugal pumps.
The key is to make sure that ALL AIR is completely removed from the unit before plugging it in. The easiest way to do this is - with the unit assembled and the drain (intake) line inserted into the tank - draw a vacuum on the return line (i.e. remove the end of the return from the tank and suck on the end) until you see water freely flowing down the drain line from the tank to the canister filter and then settle somewhere up the height of the return line on it's way back to the tank - if you hold the return line above the water level in the tank, the water level in the return line should stabilize around the same level of the tank. THEN turn the pump on.
