Originally Posted by serfty

At SYD T3 look for a check-in counter with the banner "Domestic Connection to International" or similar. (Not sure where it would be in SYD, ask if you can't see one[stress International connection]).

You check-in there, showing your PP/Travel documents etc and you won't see your luggage until Singapore.

Transit in MEL is easy, don't go down to arrivals, head up to the central departures area look to the left side of 'security' and follow the signs to "International".