Once we had to turn back and dump 80T of fuel after
one of the first class pax had a heart attack. LAX ATC
vectored us over the Pacific and insisted on 6,000 min
altitude (which corresponded to our QRH and SOP
requirements).
6,000 was also for the 727 in Oz so that altitude has
always stuck in my head. Haven't flown a dumpable
aircraft since so my thinking might be outdated a tad.