@RustyRatRod pointed me in the direction of the factory repair manual (insanely better than the Hayes I have by the way...) it appears that second line is the vent that used to run to a charcoal canister which has since been deleted. I'll try your idea about the ethanol free route but I'd still like to figure a way for adding a vapor return line as a fail safe. Would I just look for a sending unit with a return line built in?