I am replacing the gas tank on my 1980. The.. previous owner was my grandfather. There are three nipples coming off the gas tank sending unit thingy, and one of them I presume is a vent for the fuel vapor for the canister. That stuff is since been long gone on the truck. He had it plugged, but Im guessing some of my fuel issues was having a gas tank that couldn't vent... on top of the rust and bad gas gauge unit haha! What should I do to it?