Sure is hard to get fuel to run against positive air pressure (about 10-20 lbs)
That's what I used to think! But JohnG is correct, the dynamic pressure at the speeds we fly ain't that much. Isobar #1 would routinely land with fuel sprayed all over the side of the fuselage behind the fuel vent (it was oriented into the local flow for fuel pressurization reasons). I was always amazed that fuel could travel "upstream" like that!