Mysterious rusted line by brake lines! Help!

[lemonlyme]

Hey guys what is this third line above the brakes that has been snapped off for some time. Tried to follow it up to the front of the vehicle and it's snapped off there as well

 

[pc1p]

I think I just saw this on Facebook...

But anyways, what year truck? It could be a gas tank vent line, but I haven't seen this on my 4th Gen so I don't know exactly...

 

[junkyardbiker]

Is it maybe the LSPV return line? like someone has tried to bypass it?