Inline between the fuel pump and the engine is the fuel pressure regulator/filter combo unit. This has an inlet fitting and return fitting on one end and an outlet fitting on the other end. The high-pressure fuel feeds into the unit, where it is regulated to 58 psi. What fuel isn’t needed is returned to the tank, while the regulated fuel feeds through to the fuel rail on the engine. The return line will be plumbed into the fuel tank via a splice in the fuel filler neck.