I have spent the last 30 odd years trading throughout the world including Australia. The standards in Australia are not the same as the EU. Any product that comes from the EU and is shipped to Australia has to comply with Australian standards (which are tough) and any product that comes from Australia shipped to Europe has to comply with EU standards and if it does it can circulate within the EU countries.
However, there still have to be customs checks because Australia is not in the Custom's Union.
The UK wants to leave the custom's union and trade on WTO rules. WTO rules dictate that there has to be a hard border.
Australia, however, is a good country to bring up because about 20 years ago it took about 5/6 weeks for shipments to reach there - now because there are fewer ships, everything is shipped through hubs, containers are trans-shipped from vessels to vessels and ports to ports. The last shipment I shipped to Australia a couple of years ago took over 4 months because of massive congestion in Shanghai.
Trading with Europe is on a short-term basis where everything is time dependent and delays in documentation (which will be necessary) will cause untold delays, whereas if you are dealing with a country a long distance away you have all the time in the world to get the documentation you require.
Nevertheless customs checks are only a part of the problem that will be caused by the UK leaving.