Also, one "quirk" of Changi airport is that security is at the gate. So when you arrive at the gate for your flight to Sydney there will be a handful of xray machines and you will go through a bag check just as in other airports is done after you have checked in. Also, flights to Australian ports do a manual check of hand luggage for liquids. So allow time for this (it's quick) and don't buy water or duty free booze at AMS or on your first flight.