To make water: a childish expression; as, Mammy, I want to piddle. Piddling also means trifling, or doing any thing in a small degree: perhaps from peddling.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
Picture Frame * PieceNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes