To lay pit and boxes into one; an operation in midwifery or copulation, whereby the division between the anus and vagina is cut through, broken, and demolished: a simile borrowed from the playhouse, when, for the benefit of some favourite player, the pit and boxes are laid together. The pit is also the hole under the gallows, where poor rogues unable to pay the fees are buried.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
Pit * Pitt’s PictureNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes