BB fuel pump/lines

[cheyenne10]

I searched the boards but did not find the explaination for the 2 inlet lines on the stock fuel pump. I beleive on the tank sending unit there are 2 lines leaving tank and both hook to fuel pump. Trying to start truck after an extended period and have uphooked tank and fuel tank switch and trying to pump fuel from gas can. No fuel present yet and carb inlet line. Fuel pump is in tight quarters so R/R is discouarging. Also will be pulling motor for swap after I get it running and compression test and once over.

Also are small block and BB fuel lines the same size on 71/72 trucks?

Let me know what you can.
thanks.