Green’s Dictionary of Slang

(US) to work as a commercial traveller.

1834		‘A late Merchant’ Perils Pearl St 57: Perhaps the most laughable scene of drumming is that wherein one city merchant attempts to drum another [...] for so eager are certain of the drumming class, that, whenever they meet with a stranger, they do not wait to ascertain whether he is a country merchant or not; but, taking it for granted he is such, forthwith endeavor to gobble him up before he is appropriated by any of their fellow drummers.
1884		A. Doten Journals 1849-1903 (1973) II 1 Sept. 1534: Met & ran with George M Stewart [...] on one of his regular drumming trips for Hall, Luhrs & Co.
1897		A. Doten Journals 1849-1903 (1973) III 3 Feb. 1940: George Millar, formerly of Austin, in town—drumming for crockery.
1938		M. Rand ‘Clip-Joint Chisellers’ in Ten Story Gang Aug. 🌐 The rest of his time was spent drumming his wares in the New England territory.
1949		A. Miller Death of a Salesman 81: A salesman eighty-four years old, and he’d drummed merchandise in thirty-one states.
1960, 1975		Wentworth & Flexner DAS.
1986		L. Heinemann Paco’s Story (1987) 61: Salesmen drumming Snap-On tools and CBs, Bibles and other inspirational literature.