Wally Grout, n. — Green’s Dictionary of Slang

Wally Grout n.

[rhy. sl. = shout n. (1a); ult. Aus. wicket keeper Wally Grout (1927–68)]

(Aus.) one’s turn to buy a round of drinks.

1993

B. Moore Lex. of Cadet Lang. 437: your Wally Grout rhyming slang for ‘your (turn to) shout (the drinks).’.