The inlet pipe is barely drawing in any water.

The pipe that pushes water into the tank is flowing just fine, however, the inlet pipe which draws water out of the tank is only trickling water down the tube. I have tried numerous things and I can't get the water to flow properly down the inlet tube. The water just trickles down the inlet tube but flow perfectly fine down the output tube.

A: Water is drawn up the inlet tube from the aquarium by the siphoning action created by gravity. Once it flows into the rotor/impeller area and the unit is plugged in it will begin to pump the water out of the filter and back into the tank. If the inlet side is blocked eventually the rotor/impeller will have nothing to pump and the unit will just run dry and pump nothing.

So, based on your description water must be flowing through the system properly or you would not have good flow from the discharge side. You might want to view the setup video at the manufacturer's (Mars Fishcare) web site to make sure you have everything setup correctly.