Fuel tank pressure system

I have a 1990 Bounder 27D on a 1989 P30 chassis and 454 Carbureted engine. It has a California smog system. Can anyone tell me where the pressure line from the engine to the fuel tank starts and possibly where it runs down the chassis to the tank? I have no idea how the pressure is generated, I would like to know that too.

I no longer hear a rush of air when I remove the filler pipe cap. The cap passes the CA smog test so I am assuming the cap is good.