On the 744 it didn't come from the dump pipe, It came from the outboard surge tank vent ( NACA scoops )
Quite common out of LA when the Engineers used to squeeze all the fuel into the tanks they could on 15 hr flights requiring full tanks.....I can't recall exactly what they did to squeeze in an extra tonne or 2 of fuel but after the LAX airport authority complained about fuel spills during taxy out and takeoff they stopped the practice.
Anyway this 767 had a different issue