Green’s Dictionary of Slang

1. to dispose of, to sell, to get rid of.

1968		N. Heard Howard Street 68: Tomorra, after we down the watch and ring to Gus the Fence.
1971		R.D. Pharr S.R.O. (1998) 213: It’s hard as hell to down twenty-four pistols even in Harlem’.

2. of a pimp, to situate a whore on the street.

1969		‘Iceberg Slim’ Pimp 107: That stem must be a sonofabitch. I gotta’ down her there. It’s where the scratch is.
1972		R.A. Wilson Playboy’s Book of Forbidden Words.