My current pump looks like this:

I am trying to swap to an electric inline pump and external fuel pressure regulator for my Weber carb and I was going to plumb the return for the regulator into this factory third, smaller diameter line that was connected to the fuel pump. However, I am having my doubts as to whether or not this is actually a return or if it could possibly be something else. Also, there is a another small diameter hard line at the firewall connected to what I assumed to be the charcoal canister (mounted low down by the strut tower) - but even this I am not sure about as my manual says liftbacks have the canister closer to the front bumper and mentions nothing about wagons.
Can anyone tell me if I am safe returning the regulator bypass through this small diameter hardline going to the back of the car? Thank you all for your time and help!