The procedure to go from South Terminal to T1 is a bit less straightforward...
You need to go to the departures level and wait outside door "4" at the drop-off area. A small ~25 seater bus will eventually turn up and park just past door "4". It won't have any specific signage to suggest where it's going so you may have to ask around.
If anyone's interested, I can share some thoughts on the new terminal