mopper-up, n. — Green’s Dictionary of Slang

mopper-up n.

[they ‘mop up’ liquor]

(Aus.) a drunkard.

1919		W.H. Downing Digger Dialects 34: mopper-up [...] (2) a drunkard.
1924		(con. WWI) A.G. Pretty Gloss. Sl. [...] in the A.I.F. 1921–1924 (rev. t/s) n.p.: mopper-up. A drunkard.
1933		‘William Juniper’ True Drunkard’s Delight.