Originally Posted by
787fan
1. Do I clear immigration/customs at SYD or MEL? Do I stay on the plane or need to re-board after they clean it ?
You will clear immigration in MEL in both cases.
On the way there you'll need to de-plane in SYD, go through security in the transit area, and then re-board. You'll likely board the same plane, although it's possible that it'll be a different one (normally the LAX flight continues to MEL, but sometimes it's the SFO one).
On the way back I'm fairly sure you don't have to go through the transit area (and thus no security) in SYD. Again you'll probably board the same plane (MEL-SYD normally carries on to SFO), but it's possible you won't.