mech fuel pump return line needed or not

well i am lookong at running my fuel line now and was looking at my caddy fuel pump it has a return line, the tank i have in the back only had one pickup line.
what is the purpose of a return line in this case ?? i would guess to prevent vapor lock but not shure. i have seen a lot of gm cars with only one pump inlet also and they work fine.
can one t the return and inlet and will the fuel pump function ok or will i have to run two lines from the tank?
the tank i have has 3 big Vent tubes (from a ihc scout) so could always run the return there but if i dont have to i wont.
anybody out there dealt with this before???
springs comin stormed here yesterday couple inches of snow

Usually, only fuel injected cars have a return line.

i know what you are talking about but this pump had a return line to the tank. i did a little treading and i think it is a vent line of some kind. i am going to start the car without it attatched and see if it pukes fuel out ,if not i will leave it or cap it.

my 1982 k5 blazer has the return line you're referring to. and yeah, it will puke out fuel. but, i've run it capped off with no adverse affects (not anymore).

My somewhat-less-than-perfect memory tells me that many fuel pumps had vapor return lines. Before fuel injection, but after smog rules.

it seems to be working good with it plugged off, i tested it with it open into a jug and it seems to bypass a little bit but not a lot. never did check fuel pressure though ont he main line.

I had the bypass line on my fuel pump on my 73 blocked off and it ran fine.

I'm running a electric out of tank pump right now. I think I picked it up from Advanced for like 20 bucks or something. I think its much more reliable but just a little noisy unless you mount it in rubber.