flush, n.² — Green’s Dictionary of Slang

flush n.²

[pun on poker flush, five consecutive cards of the same suit / SE flush, i.e of a lavatory]

(N.Z./S.Afr. gay) a group of homosexual men, e.g. when escaping a police raid on a public lavatory used for soliciting.

2003		K. Cage Gayle 70/1: flush n. a group (of queens) (A flush of Queens).
2010		W. Ings ‘Trolling the Beat to Working the Soob’ in Int’l Jrnl Lexicog. 23:1 65: [A] collective noun in the 1960s for a group of men rapidly leaving a toilet at the time of a police raid was a flush of queens.