The 420 bus services Sydney Airport, but this doesn’t run to or from your CBD. The 420 operates as many as Mascot, or Burwood in the alternative way. You can take a bus from Sydney Airport to Mascot and hook up with the City by using coach as we’ve outlined https://sydney-international-airp46737.illawiki.com/1060123/sydney_international_airport_taxi_limousine_an_overview