Green’s Dictionary of Slang

(US) extracting waste (usu. food but also documents) from dumpsters.

1983		Longview News-Jrnl (TX) 22 May 12-D: I don’t know if I’d quit dumpster diving [...] I’m preventing waste, feeding myself, and feeding a lot of people that wouldn’t eat.
1990		Press-Democrat (Santa Rosa, CA) 1 Apr. D1/1: Go ‘dumpster-diving’ for soggy but still warm burgers behind fast-food restaurants.
2000		Dly Jrnl (Franklin, IN) ‘One Man’s Trash’ supp. 4 Jan. 3/1: $790 million in credit card fraud was the result of ‘dumpster diving,’ groing through trash to find account numbers.
2019		D. Winslow Border [ebook] Jacqui prefers her Washington Avenue home because the dumpster diving is better. Not only is there the Best Western, but Picnic Pizza is just up from the bridge.