Name this hose!

[blageo23]

There is a hose I disconnected from my 2G that went from the emisions stuff below the batt. to some unknown place down the fire wal. It went down right below the battery and followed the same path down as i believe the brake lines or maybe the fuel lines i dont remember. I believe I may have been told that it went back to the gas tank? what do i do with this hose? right now i just have it caped off.but maybe thats why my car is retarded i dont know.
Thanks,
Mike

[Raptor]

Gas tank vent. Don't cap it, run a new one from the tank out the back of the car through a small fuel filter like from a lawnmower. The Purge can used to be it's filter.