chamber of commerce, n. — Green’s Dictionary of Slang

chamber of commerce n.

[SE chamber, a lavatory + pun on business n. (2)]

(US black/campus) a lavatory.

1900		E.H. Babbitt ‘College Words and Phrases’ in DN II:i 26: chamber of commerce, n. Water-closet.
1944		‘Jiver’s Bible’ in D. Burley Orig. Hbk of Harlem Jive.
1960, 1975		Wentworth & Flexner DAS.