Green’s Dictionary of Slang

(Aus.) the buttocks; the anus.

1983		R. Aven-Bray Ridgey-Didge Oz Jack Lang 9: He reminded himself that he would not put his deaf and dumb on the brasco.
2014		D. MacShane Prison Diaries 359: Del tries to improve my rhyming slang knowledge. I know what ‘deaf and dumb’ means though I have yet to experience what is called a cavity search.