I don't use a manual valve as here is a solenoid already doing the work. Adding stuff adds potential leak points. The thing about going 6mm to the pump is to reduce pressure drop on the suction side and put all valves, filters, solenoids, reductions etc on the pressure side. Even top grade builders forget about this and adds up many connectors on the way through the fuel system. I always try to keep the lines as uncut as possible.