How is the fuel tank vented

[palmtree]

I seem to be getting some sort of vacuum in my fuel system. I was having trouble starting it and so I installed a bulb style hand pump and some clear lines so I could see what is going on. If I have someone crank it over while I pump the bulb it will start and run. Then when I shut it down I can barely hear the squeak of some air getting in and will slowly see bubbles forming in the clear fuel line. If I try to start it without someone pumping the bulb then I can see the bubbles just sitting in the line. Fuel doesn't seem to move (I assume it is air locked).
I can't tell how the tank is vented. I have a hose that runs from up near the filler neck and hangs down open near the tank. Should the open end of this line be attached to the tank somewhere?
Any ideas?