My 1986 Silvarado has an auxiliary gas tank and the existing open and close valve between the two tanks is not working. I want to install two manual shot off valves, connect the two line with a “t” and attach the two valves some where under the bed where I can reach them…switch one off and one on when switching tanks…but, I cant find a 3/8 shut off valve at local auto stores…any suggestions? thanks, Ray