Gas leak from the drivers side fender???

[ehuth1]

Went out filled the truck up (aux tank in the bed) then went for a short cruise. I pull into the driveway, then backed up to re-adjust to the garage entrance and noticed a (splat, splat, splat, bluuuuuuuuuuuuuush) puddle marking in the driveway...? Before I can get out it's evaporated... So I proceed to leave it outside to do it's thing and pop the hood to find out it's coming from a small black canister on the drivers side that has a fuel line ran to it... Looks like it has a line going back to the fuel pump, but everyone I ask don't have a clue as to what it is. It's stopped leaking for now, but if it continues the wifes going to kick her (the truck) outside!!!!!

Someone please educate me on this mishap? I'm a newb, but I've already used the search button.

Thanks in advance.