Green’s Dictionary of Slang

(Aus.) rum or the cordial Bonox and rum.

1941		Aus. Women’s Wkly 26 July 22/2: The rhyming slang of the Cockneys still has its adherents [...] ‘Dad and Mum’ for rum.
1968		J. Alard He Who Shoots Last 96: I’ll have a dropa dad and mum dis time.
1992		R. Puxley Cockney Rabbit.
2002		Pete’s Aussie Sl. Home Page 🌐 Dad and Mum: rum, Bonox and rum.