I have a 45 gallon aux. tank and solenoid valve on mine and flip the switch inside when I need it and turn it off when I'm full. On my 2003 I just had a manual valve and left it open all the time and after driving ~150 miles my fuel gauge would show empty but once the aux. tank ran empty and my main tank level started dropping the fuel gauge would start showing a level again.
2018, 3500, SRW, LTZ, Z-71 4X4
Passed down to my son - '03 Silverodo LT, CC, D/A, 4X4, Hypertech, Rino, Bilstiens, TTT's. Eric's pump upgrade, 4" MBRP exhaust, AFE Intake.
2015 Camaro SS2
'06 Mobile Scout 31 BWFS 5th wheel
Owner @ Port Allen Tire & Service