True.
But how do we know we're not dumping slush into 2&3?
Part of the problem with the 777 were stagnant 'dead' zones in the tank where slush could accumulate.
Does the 747 have 'stirrers' in the tanks?
I have no idea how long it takes from a full fuel load and a normal climb profile to burn the CWT empty and the 2&3 Main tanks down to 18,200kgs for the gravity transfer to take place.
Do these transfers lines run through tank 1&2 and therefore 'preheated' by warmer fuel?
How does Boeing prevent 4000kgs of slush dumping into 2&3?