Green’s Dictionary of Slang

(S.Afr.) a gulp, a swallow.

1972		‘Rawbone Malong’ Ah Big Yaws? 47: Gimme a sluk ivyaw Pipsie, mehn.
1977		C. Hope Ducktails in Gray Theatre Two (1981) 51: Have a sluk.
2005		A. Lovejoy Acid Alex 166: A six-shooter is also known as a six-man can and is a bottle of cheap wine. Every now and then he stops and takes a lekker sluk.