Green’s Dictionary of Slang

1. a brothel, or a whore’s vagina .

1781

Belle’s Stratagem 13: Mrs Racket: Here’s to every upright member that enters the House of Commons! [...] Courtall: With all my heart, Bet — And to every upright member who enters houses that are not common.

2. a privy, a lavatory.

1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue.
1811		Lex. Balatronicum.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.
1860		Hotten Dict. of Modern Sl. etc. (2nd edn).
1864, 1867, 1870		Hotten Sl. Dict.
1873		Sl. Dict.