Your mob may have a different fit, but from memory the -400's I have flown have about 5.2t capacity, which is not 45min worth of fuel.
For reference to aid in your discussion.
Horizontal Stabiliser Tank capacity of the 747-400 is as follows.
(SG approx .802)
Gallons:- 3,300
LBS:- 22,110
Litres:- 12,492
Kilograms:- 10,029
