Stop in for a cup of coffee

Ok dumb question....

My Demon fuel tank has 2 rubber fuel lines coming from it. 1 to the electric fuel pump, I get what that one is, be nice.. there is a 2nd one up towards the top. I dont think these had a return line, so is it just a vent? Where did it run to? Filler neck? The line is about 6-8" long with an Otiker clamp on the end. Just a breather supposed to be there? Any help would be appreciated as then I can put gas in for the first time and fire it up.
'71 ? 49-state car? My guess would be vent - maybe into the fill tube via a small hard line.