Green’s Dictionary of Slang

1. (US) the mouth.

1846		Swell’s Night Guide 77: This was followed by a munzer; for Bet’s only answer, was a prop in the jowl; she tapped his blow-hole and he spouted red.
1950		‘Hal Ellson’ Tomboy (1952) 111: You shut your blowhole.

2. (Aus.) a talkative person.

1919		W.H. Downing Digger Dialects 12: blow-hole — A garrulous person.
1955		N. Pulliam I Travelled a Lonely Land (1957) 230/2: blow hole – an overtalkative person.
1960		(con. 1940s) G. Morrill Dark Sea Running 33: He put up with that other blow-hole, Army Lieutenant Drupp.

3. (US) the anus.

1947		‘Imaginary Diseases’ in AS XXII:4 Apr. 305/1: conjunctivitis of the blowhole. This one is in very common use and has several variants, among them Acidosis of the Blowhole, etc., etc. It is invariably used in a derogatory sense in reference to any person who complains of being sick. Any suspected malingering or hypochondria is instantly diagnosed as ‘a bad case of conjunctivitis of the blowhole.’.
1960		(con. 1940s) D. MacCuish Do Not Go Gentle (1962) 340: It makes the ole blow hole pucker up.
2003		McGill Reed Dict. of N.Z. Sl. 89: go kiss a cocky’s blowhole A rude way of telling someone to get lost.