Quote "When the center tank indicates 0 the tank is virtually dry. I have pumped the fuel out of the tank to the 0 mark and gotten less than 5 gallons out of the sumps at the end.
With the plane flying there is a nose up attitude which keeps the pickups in the fuel. It's almost all usable (barring turbulence).
Without meaning to burst ya bubble if you only got about 5 gallons out of the drain (who said it was at the lowest point of the tank on the ground i.e nose down attitude)put a nose support jack in position and level the A/C and see how much you get out.You may be very surprised how much is still there if you have to get into the centre tank..