[Shon]

The one line that is coming from the tank that is actually going INTO the tank is where you put your pump and then the vette unit. and from the vette unit you will run the return line to your tank and the other one up to the fuel rail.
you want the pump probably as close to the tank as possible, I have mine mounted on the frame rail.
You will want to go to Napa or the like and get some dorman brand hard line that snaps into that vette unit and then I used rubber EFI hose and clamped it on those hard lines using the EFI clamps too.

That other line you say is going to your tank is a vent tube probably. if that is the only vent tube to the tank I would leave it alone but if you have more than one you 'MIGHT' can use it as the return line. I just ran a new line and my tank behind the seat is an emissions tank so it has a nipple on the filler neck I put the return line to.