One whose business it is to empty necessary houses in London, which is always done in the night; the operation is called a wedding. See Wedding.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
Nightingale * NigmenogNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes