I have been wondering that before the advent of modern fuel injection delivery systems on automotive engines, how vehicle engines were first started at the end of the automotive assembly line. Years ago engines used carburetors and the entire fuel system would be dry. If the fuel system were not primed in some fashion it would probably take 30 seconds of starter engagement spinning the engine to get sufficient fuel into the carburetor so the engine would start and vehicle driven from the assembly line. I am thinking that several pounds of air pressure were applied at the fuel tank filler neck. This pressure would force fuel through the line, through the fuel pump and filter and into the carburetor float bowl. The bowl chamber would fill with gasoline and then the float would rise and stop fuel entry at the designed fuel level. With a full float chamber then a quick, cold start would be possible. But this is a guess on my part. Does anyone know exactly how carburetor equipped vehicle fuel systems were primed on the assembly line.