Truck Repair: fuel lines, vent tube, vent system

Question

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Followup To

Question -
i have 95 pete drive shaft fell out and busted fuel tanks. had fuel tanks repaired and connected  and i need to know how to tell if i got  my fuel line crossed or not when hooking  them back to my tanks. engine will turn and run for a min or two but wont stay running. fuel filters are  getting fuel.

Answer -
Do the fuel lines exit the top of the tank?


line at bottom to fuel pump, line at top feeds the tank. fuel goes from right tank to left tank leaving left tank empty. the next day fuel leaves right tank to left tank leaving right tank empty.
peterbilt place can not figure out why it would do that. they said even  if there is something wrong with equalizer valve, it should't be doing that. our only option is to turn off the valve at the bottom of one of the tanks. (both are primary tanks)and cap the top line.  

Answer
The only instance I have experienced with fuel returning to one tank was related to the tank vent system --- vent tube closed or vented cap bad -- CAT engine? -- Run the fuel down -- with the engine running look down into each tank and see what is happening in the tank with the return lines --