dumpster diver
n. A person who sifts through garbage, particularly a dumpster, looking for valuable or useful items.
Other Forms
Tonight, however, Seymour's van follows a proven route, and each Dumpster diver has a proven style. Larry has a sweet tooth, and is more of a window shopper — peeking through the Dumpster opening, but rarely climbing in. The gangly Ard is less squeamish, though he uses a stepladder to get in.

There's only one "bottom of the Dumpster" diver on this team, only one who takes literally the Dumpster diver's credo: "The best stuff is always at the bottom." Yet for all his abandon, Straight Edge Ben — so nicknamed because he doesn't use alcohol, tobacco or drugs — is the choosiest.
—Lorraine Aheard, “Word for food,” The News & Record, January 20, 2002
So-called ‘dumpster divers’ have sometimes gleaned valuable information—carefully protected on disk—from discarded papers.
—Computer Decisions, May 7, May 07, 1985
1982 (earliest)
Restaurant and store owners have complained about drunks panhandling during the day and "dumpster diving" through trash at night.
—Phil Long, “Special wing for drunks suggested at future jail,” The Miami Herald, November 24, 1982
John Hoffman, author of the book The Art and Science of Dumpster Diving wrote to me with a theory about the originator of this phrase:
It is my opinion that a "diver Callaghan" was the originator of the term and he ran a FOOD BANK and was written up in NEWSWEEK or TIME in 1978, 1979, approx, when he got some kind of award from the government.