Originally Posted by phunk

Typical fuel hose from the 90s would permeate but I don't believe the modern nylon and Teflon hoses they use will permeate. I at least know that if it does permeate, it's a small fraction. But I cannot say with certainty that it doesn't at all. I believe that the evap of a return system has more to do with the heating of the fuel that is effectively cooling the rails and bringing the heat to the tank. Then again, the evap in the tank gets vented to the intake manifold eventually other than the pressure that escapes when you open the gas cap.

This forum is probably the wrong venue to get proper details on emissions systems since it's the last thing most tuners think about or study!