Hi,I have an Australian passport and I'll be travelling to Beijing this August

and will be returning to Australia in September, therefore require at least a single-entry visa for sure. I also want to travel to another country from Beijing. If I book a return flight to the 3rd country, can I make use of the 72 hour free transit in Beijing and leave Beijing within 3 days after coming back from the 3rd country? If so, my flight back home requires me to transit in HangZhou, but I understand that I have to leave from the airport where I get the free entry (i.e. Beijing). I'm a little bit confused as to whether I need a visa with multiple-entries or can make use of the 72 hr free transit. My flight back home would be MU711 from Beijing - Hangzhou - Sydney. Can someone help clear up the confusion for me? Thanks