Just run your lines from the tank you are using to the fuel pump. Use a single hose from the tank your using by connecting it to the metal line from the tank to the metal line to the fuel pump (3/8" supply, 5/16" Vent, and 1/4" return), You need about 12" to 18" of each size fuel hose and 2 clamps for each hose. You can direct wire the Sending Unit on the tank you are using to get the gauge to work unless it is bad or other problems exist. There have been threads in this forum on this very subject that you can look at for any additional information.
Have a question, why do you have one tank on your truck and a fuel tank selector valve?