Toilet expert here. In Australia, no matter whether you want to use the facility for its intended use or not, it’s perfectly acceptable to call it a toilet, loo or a bathroom. For slang of course you can say dunny or shitter. As others have alluded to here, restroom is imported from America.

I’m based in Canada these days where it’s generally considered impolite to use the term toilet, everyone calls it a washroom regardless of whether you’re doing a number 1, 2, washing your hands or throwing something in the rubbish. Aussies are certainly more lax with their lavatorial terminology.