fuel system help please

[vegas_k10]

sorry for being short but im in a hurry. I have a 77 k10 and my fuel sending unit has 2 outlets. 1 obviously is the pickup, is the other a vent or what?

i dont remember when i took it off what was on that one, but now im having problems. I took the screen off the bottom of my pickup in the tank, put it back togeather, and its not getting fuel from the tank. If i blow into the fuel hose that goes into the tank i hear air with 5 gallons of gas in it, and i should hear bubbles. anyone got a clue????