Uh...I think you might be confusing two subjects. (or maybe you're not). You don't need a return line UNLESS you are using a purge valve. Then, you need to put this fuel somewhere.
Now, you don't need the dual Andair valve, but it helps. I've plumbed both. Without the dual valve, you just run the return line to one of the fuel lines prior to the valve. In this configuration, you need to remember to select the other tank when you run the fuel pump and have the purge valve engaged.
With the dual Andair valve, you can purge and return from either tank and you don't have to remember or placard for that.