Green’s Dictionary of Slang

(S.Afr.) a non-returnable 340ml (12fl oz) beer bottle.

1966		Daily News 12 Sept. 2: The squat bottles popularly known as ‘dumpies’ [...] are non-returnable, and deposits are not levied on them at times of purchase [DSAE].
1973		Eve. Post (Port Eliz.) 19 May 1: Apart from the 30 men on the field at any one time, exuberant supporters packed the stands, a girl in one hand, a dumpy in the other [DSAE].
1989		East Province Herald 3 Nov. 1: Since yesterday, a shortage of pint bottles has been hitting bottle stores and bars, and drinkers will have to switch to dumpies for at least a week [DSAE].
1996		CyberBraai Lex. at www.matriots.com 🌐 DUMPY: You may drink your dop out of a dumpy or dumpie, which is a perfectly-named small, fat beer bottle.
2003		‘SA English’ on Joburg.org.za 🌐 Dumpie – A South African beer served in a brown 340ml bottle. An example of usage is: ‘Hey bru, throw me a dumpie.’.