75' Fuel Return Line

I recently replaced my fuel sender and it has the extra nipple for a return. I am currently running a single-in, single-out fuel filter which I thing is the original 75 set-up. The PO removed all the emmissions equipment (Charcoal Cannister Included) but there is a unused non-metal hard line running from the engine compartment to the rear of the Jeep near the tank. Can I/Should I replace the fuel filter with a 3-nipple one and run a return back to the tank? Is this other non-metal line acceptable or is it only for fuel vapor?

 

My 75 has a hard line to the tank for the vent. I use a filter that has the outlet to connect.. You could connect it, but getting the tank out to access the fitting is a real PITA>>

 

I would run another hard line (btw, if it ain't metal, it ain't hard line.) I wouldn't trust the old vent line to carry liquid, it's very thin walled and relatively easy to damage.