They use a special filter that has a return line that goes back to the tank.Randy,The problem with the one line system[no return line] is that it's harder on fuel pumps.They don't like to be "deadheaded" when you're dealing with the pressures that are needed[50-60 psi].Carl McQuillian told me that the new Holley ecm's learn really fast. Heretofore it took nearly 400 miles for them to fully learn.He said that the new ones come in in about an hour.
corvettes use one line and a filter at the tank. the filter does something that cuts the need for a return. when i had a ls3
put in my vette they used that filter. jim