Make the cull easy or quiet; gag or kill him. As easy as pissing the bed.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
See also the definition in Nathan Bailey's 1721 dictionary of canting and thieving slang.
earth bath * easy virtueNathan Bailey's 1721 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes