Mrs Chant’s, n. — Green’s Dictionary of Slang

Mrs Chant’s n.

[rhy. sl. = my aunt under aunt n.; ult. Mrs Ormiston Chant (1848–1923) a well-known moralist]

a lavatory; thus visit Mrs Chant’s.

1960		J. Franklyn Dict. of Rhy. Sl. 97: ‘I’m going to see Mrs. Chant,’ rhyming with ‘I’m going to see my aunt’, which is euphemistic for going to the W.C. [...] more frequently employed by women.
1972		Dodson & Saczek Dict. of Cockney Rhy. Sl.
1992		R. Puxley Cockney Rabbit.