My hydraulics business goes to Swedol - discount, you know.
I don't really think that the size of the return line is the problem. The normal setup for this winch is pump - winch - steering box - back to pump. So with a standard setup, there is no option to use anything but a pressure hose.
Anyway, my manual valve simply creates a bypass directly back to the pump, so there are no restrictions or one way valves in my system.
Well, I'm not closing any doors, I will test a bigger diameter return hose later.