In the 19th century, one type of scavenger in London were the "pure finders": "pure" is another word for dog feces. They would scavenge dog feces from the Thames (which was, at the time, a giant sewer) and sell it to tanners, who would use it to clean leather.
|Not a precise picture of a pure finder, but a mud lark, another scavenger of the Thames. |
Picture from London Labour and London Poor (1861)