Green’s Dictionary of Slang

waste paper basket.

1884		Referee 2 Mar. in Ware (1909) 257/2: If the criticism or remark is nice, I read and enjoy it ; if it is nasty, it is thrown into the W.P.B., and it troubles me not.
2000		S. Maloney Big Ask 113: I crushed the slip into a ball an tossed into the nearest WPB.