Hi Welchy,
I cant see why an air lift/venturi would not work(for twenty litre drums that were full), but for the 44 gallon drums we use a different method.
On the top of the 44 you have the two bungs, in the big bung we made up a long pipe/spear that screwed into the bung hole and was long enough to all but touch the bottom of the 44, in the small bung hole we screwed in a air regulator and pressure relief tap.
Snap you delivery hose to the bung with the spear, air hose to the regulator 2 to 4 psi pressure and the fuel will flow freely, watch the top of the drum and if the top starts to swell, open the pressure relief tap to get rid of pressure build up and close again for continuous fuel flow.
cheers duggie