Evergreen don't say anything about filling the 747, but it seems to imply that it fills on the runway. The requirement for a 2500m runway is slightly restrictive, but with a 747 cruise speed it should be feasible to run out of capital city or military airports. They say it holds 78,000 litres. I think that might be equivalent to 23 Dromader flights. I can imagine the logistics of filling rapidly might be complex. That might be 3 semi-trailer tankers on the ground and they seem to add retardant chemicals.
On the other hand, it can basically get here from the US overnight.