Fuel tank fitting.

[tourbox]

It could be a vent line but usually the tank vents through the cap. It could also be an overflow line when filling the tank. Look at your gas fill area of the tank for a hole in the spigot area. See if you can blow air through it to the line you are concerned about.
tourbox

 

[pitbullsuperglide]

There is a little overflow tube under the gas cap. I believe they are connected.

 

[Jack Klarich]

I looked at the other bike again and i think its probably a vent. The hose on that bike goes towards the back of the bike under the seat. Maybe i should put a hose on it and direct it to the back.

If I remember right the tank vented down the backbone under the seat, the OE carb vented just ahead of the swing arm straight down