Green’s Dictionary of Slang

the gallows; thus knock down/up for the crap, to sentence to be hanged.

1789		G. Parker Life’s Painter 137: He was knocked down for the crap the last sessions.
1793		Bacchanalian Mag. 43: Bad luck to every snitch, say I, / Afraid for himself to touch the cly, God send they at the Crap may die.
1812		Vaux Vocab. of the Flash Lang.
1828		Lytton Pelham III 298: A square crib, indeed! aye, square as Mr. Newman’s courtyard – ding boys on three sides, and the crap on the fourth!
1830		Lytton Paul Clifford III 126: I’ll go to the crap like a gentleman, and not peach of my comrades.
1840		T. Haliburton Letter-bag of the Great Western (1873) 105: You are too fond of drink, and keeping company with needy mizlers to kepe secrets for any wun without bringing him to the crap.
1949		Monteleone Criminal Sl. (rev. edn).