Green’s Dictionary of Slang

the anus, the rectum; esp. in contemptuous/dismissive phr. stuff it up your clacker.

1960		J.E. MacDonnell Don’t Gimme the Ships 135: Come on then up there, off your clackers!
1967		‘Whisper All Aussie Dict.’ in Kings Cross Whisper (Sydney) xxxiii 4/3: clacker: Posterior.
1983		R. Aven-Bray Ridgey-Didge Oz Jack Lang 22: Clacker Anus.
1998		Bug (Aus.) 16 Aug. 🌐 When they were sticking those syringes full of morphine derivatives up the cheeks of your clacker [...] what did you think it was?
2003		www.djnomc.com 🌐 Film treatments, stories, songs and jokes comin’ out my clacker. Clacker is an Aussie term for anus, from Cloaca the ancient roman goddess of the sewers.
2005		M.B. ‘Chopper’ Read Chopper 4 266: Tell a sports master that he could jam his Don Bradman special edition [...] bat straight up his clacker.
2010		L. Redhead Thrill City [ebook] Just raunchy. You won’t have to stick anything up your clacker .
2016		N. Cummins Adventures of the Honey Badger [ebook] VITAL AUSSIE VERNACULAR [...] Obvious: Stands Out Like a Dog’s Clackers.