[chumbucket]

Remove your hose from the filter or the tank. Whichever is the closest just before the primer bulb. Stick that end in a five or six gallon gas can and run it that way. This will at least tell you which direction (ie; before or after the point of the disconnected hose) to work in. It'll save a lot of time and some guessing too. If it still stalls drawing from the portable tank, work your way towards the motor starting with the primer bulb. Otherwise, work your way back towards the tank starting with the water separater filter (which you should have if you don't already).
G'luck :)