To be, or have been, hard at work. Originating in Australia.
"G'day mate, how ya been?"

"Mate! I've been flat out like a lizard drinking! This is hard yakka! I've been working on it for yonks!"
by G'day and Well Hey January 21, 2009
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To be not busy.

As a visual metaphor, it implies the opposite to the expression ‘flat out’. A lizard drinking is visually flat against the ground, still, stationary, prostrate, prone and apparently inactive - the opposite of what a person is like when they are busy.

The primary definition that I heard for years amongst colleagues and friends fluent in Strine was the 'not busy' version. It was only recently that I have heard it used to mean 'hard at work' or 'busy'. It feels that the traditional components of visual metaphor and humour in the Strine lexicon have been lost or the expression misconstrued at some point.
Flat out like a lizard drinking -

"Man it's quiet here. You busy?"
“Busy? Flat out… like a lizard drinking… hehehe.”
by InterlocutorInThe1st October 27, 2020
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Adj. Simile. To be extremely busy to the point of running "flat out," a play on words involving the image of a lizard that physically stretches itself thin to literally drink water from a pond etc.
Slacking off? Are you kidding, mate? I'm flat out like a lizard drinking.
by TheBadSanta September 19, 2008
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1. verb/simile. To be working really hard, or so under the pump that you've found yourself dehydrated.

2. verb/simile. (sarcastic) Doing nothing at all.
1. How are ya, mate?
Oh, dude, I'm flat out like a lizard drinking.
Up for a brewskie later then?
Yeah, for sure.

2. How are ay, mate?
Oh, dude, I'm flat out like a lizard drinking.
Yeah righto, come out for a brewskie then.
Orright, seeya in a sec.
by Ryan Paine February 15, 2008
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