Where "The Full Bottle" Comes From
"The full bottle" most likely developed from British slang "no bottle," meaning no good or useless — a phrase recorded from the mid-19th century, with possible connection to Cockney rhyming slang "bottle and glass" (rhyming with "class"). Australian English took the underlying idea and flipped the phrase: rather than "no bottle" meaning bad, "the full bottle" came to mean thoroughly knowledgeable or expert on a subject.
"Are you the full bottle on this?" means "do you really know what you're talking about here?" — a test of expertise rather than simply enthusiasm. The phrase carries a distinctly Australian assumption that genuine knowledge matters more than confident performance of it, and that someone claiming expertise should be able to back it up.
Source: World Wide Words — "Bottle"
"Ask Dave about engines, he's the full bottle on that stuff."
How Aussies Actually Use It
"The full bottle" describes someone with real expertise or inside knowledge on a subject, as in "she's the full bottle on tax law."
It's often used in the negative too — "not the full bottle" — to describe someone who isn't fully across the details of something.
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