Why wade through mud searching for riches among the turds when you could search through the source of turds themselves – the sewers?
This was the work of the tosher, which is not only how Sean Connery says tosser, but also the name of a sewer scavenger like the one pictured above. It's like he's panning for gold, but mostly getting turds. (Unless you got lucky, and some member of the upper classes accidentally swallowed and digested some nice jewellery.)
The practice was written about by our friend Henry Mayhew, who described the work of the tosher in pretty horrifying terms:
"Many wondrous tales are still told among the people of men having lost their way in the sewers, and of having wandered among the filthy passages . . . till, faint and overpowered, they dropped down and died on the spot: Other stories are told of sewer-hunters beset by myriads of enormous rats, and slaying thousands of them in their struggle for life, till at length the swarms of the savage things overpowered them, and in a few days afterwards their skeletons were discovered picked to the very bones."
Please join me in saying: Jesus Christ!