The funny thing about VW fuel pumps is that I believe they need to have the pressure on the inlet in order to work. In other words, I don't think they can "suck" the fuel out of a can.
I built a temporary fuel tank out of an gallon alcohol bottle. I attached a quick disconnect line to the bottom of the bottle and ran it to my fuel pump. If you use a clear fuel line you (not recommended) you can see if the pump is running or not. I discovered I connected my fuel pump up wrong when I noticed air bubbles pumping into the bottle.