Same system. I try to stop my FO from setting the dump fuel during preflight on the 744 because it is a. not in the book, b. not necessary, c. a worthless procedure since any dumping after takeoff will take 45 minutes or more and so an early dumping is a waste of time, d. dumping cannot take place until the flaps are up (ar at least above flap 1), e. it is not a recall action and the setting of the dump figure is part of the checklist procedure (and you don't know whether you will dump to max landing weight, min landing weight or some other value determined by the emergency you are handling), and, e. (the one I want your advice on please) if there is a fault in the dump system, any residual fuel in the dump lines might leak onto the tarmac.
I am amazed that so many pilots I fly with think that setting the dump figure is necessary. Calculate it, by all means, but why set it?
Apologies it this is off topic, but some of the replies here show that there is knowledge out there and I want it!