As with all Boeing courses the essence is "need to know" and that applied on our B777 course with regard to the fuel system.
The normal operation with wing and centre fuel was to operate with all the pumps on. Due to the centre producing higher pressure than the wing pumps the centre would empty first (necessary for wing bending moments etc), then with around 900kgs left in the centre the pumps would become uncovered in the tank and the pump switch pressure lights would illuminate plus EICAS messages.
Centre pumps then switched off and EICAS messages obviously disappeared.The fuel feed would then transfer to the wing tanks (tank to engine, pumps already running) and would (assuming no imbalance, which was a very infrequent occurrence) remain so for the rest of the flight.
However we were never told where in the tank these centre pumps were but, one can assume they must not have been in the lowest point (cruising attitude) as 900 kgs still remained in the tanks. This last 900kgs was then transferred to the wing tanks (without any pilot intervention) by "other" pumps. No display of this part of the system on the schematic and obviously as it was automatic not included in the " need to know".
The "leaked" report talks of "water" maintenance messages in the centre tank, again something the crew were not party to (need to know) but where in the centre tank would this "water" have collected? At the lowest point?
If so, it would have still been there when the tank stopped feeding and subsequently have been pumped into the wings.
No suggestions, just facts on how the fuel system works....