Green’s Dictionary of Slang

brush n.3

[SE paintbrush]

1. a house-painter [meton.].

[UK]Hotten Sl. Dict.
[UK]Sl. Dict.
[UK]Farmer & Henley Sl. and Its Analogues.
[Aus]Crowe Aus. Sl. Dict. 12: Brush, a painter.

2. the supposed resemblance of the glass’s shape to that of a house-painter’s brush.

(a) a small glass, made of an inverted cone fixed to a thick stem, which is used for drinking drams of whisky or other spirits.

[UK] press cutting in J. Ware Passing Eng. of the Victorian Era 51/1: That little bloke [...] put away six pots of four-half, three kervoortens of cold satin in a two-out brush, a ’arf kervoorten of rum, and a bottle of whisky.

(b) strong, rough whisky.

[US]J. Lait ‘Omaha Slim’ in Beef, Iron and Wine (1917) 105: They call it ‘the rub of the brush’ in that world to which Slim belongs. They call it that because that’s the way it feels when it goes down.
Winnipeg Trib. (Manitoba) 7 Apr. 55/3: He might get something that he could sell for [...] a ‘rub o’ the brush’, a half pint of the lodging house booze.
Lancaster Eagle-Gaz. (OH) 3 June 4/4: It was talk of towns [...] of various kinds of whiskey. Milkshake recollected longingly the ‘Rub o’ the Brush’ he had swigged [...] in Chi.
[US]A. Hardin ‘Volstead English’ in AS VII:2 86: Terms used for intoxicating liquor: Brush whiskey.
[US]Orlando Eve. Star (FL) 21 Dec. 4/5: ‘Rub o’ the Brush,’ a liquor that boiled if it spilled on the bar.

3. (N.Z. prison) a prison-made stabbing weapon [the use of a sharpened toothbrush handle].

[NZ]D. Looser Boobslang [U. Canterbury D.Phil. thesis] 31/2: brush n. a knife, a stabbing weapon.

In compounds

brush mouth (n.)

(US black) a sip of whisky.

L. Turner Africanisms 232: ‘A drink of whiskey,’ i.e., ‘brush mouth.’.