Stop in for a cup of coffee

Sooo question. Anyone here ever custom plumbed a second tank into a vehicle?


My 78 has a 15 gallon tank. With 4.56 gears and 33s, and a granny 4 speed, 6-7 mpg is lucky. The truck factory has its tank on the drivers side. However my bed is actually set up for a passenger side tank(California model according to research) but also has the provisions that I can punch out for a drivers side tank. I have a spare tank so I thought about mounting both tanks but not sure how to plumb the two of them together.
Just plumb it. T it. Those tank switching valves are a pain in the azz. It will seek it's own level between the two