Green’s Dictionary of Slang

(S.Afr.) a 20-litre (35-pint) black plastic container, used for buying wine in bulk.

1980		Cape Times 28 Mar. 2: Varkie’s days are numbered. The Minister [...] yesterday asked wine producers and dealers to take immediate steps to phase out the notorious ‘swartvarkie’ 20l wine container [...] Although he did not intend proceeding with legislation to ban the ‘swart varkie’ [...] he agreed the container should disappear [DSAE].
1984		Cape Times 18 Aug. n.p.: Commemorate the ‘swartvarkie’ — that 25l. demijohn of fond memory in which dedicated vaaljapie men used to buy their tipple [DSAE].