How is fuel drawn from drop tanks in WW2 airplanes?
Like the F-86, air is supplied into the tank so the fuel can be pushed up. On the P-51, the source of the air was the vacuum pump (the one used for the flight instruments), providing 5 psi of pressure.
Knowing this, the two connectors, pressure and fuel, can be seen in many photos.


Source: P-51 manual

And the two connectors:


Source: ww2aircraft.net