I have a 14 3500 MegaCab, and getting ready to install the auxiliary tank and thinking of putting a T where the rubber hose attaches to the 3/4" overfill return line.
By doing this I will not have to cut into the main fuel fill tube. If the rollover valves are at the fuel tank I will not have to install one in the auxiliary fuel line.
Will this work??

Where is the rollover valve that prevents the fuel from coming out of the fuel tank located?

My first thought was that it is in the metal filler tube section but there is the 3/4" inch overfill return line that goes back to the tank that would also need a rollover valve.

1. Are the rollover valves in the top of the fuel tank where the rubber hose section of the fill tube and return line attach to the fuel tank?
2. Is the flap that is pushed in when fueling, the device that prevents the fuel from coming out of the fuel tank in the event of a rollover?