Green’s Dictionary of Slang

donicker n.

a privy.

1933		Ersine Und. and Prison Sl. 33: donnicker, n. A toilet.
1935		A.J. Pollock Und. Speaks 32/1: Doniker, a rest room.
1949		F. Brown Dead Ringer 11: She found the kid, Ed; fell over him in the dark [...] on her way to the doniker.
1949		Monteleone Criminal Sl. (rev. edn) 72: donneker A wash room.
1953		F. Brown Madball (2019) 27: ‘You didn’t go outside once, not even to go to the doniker?’.
1962		C. Clausen I Love You Honey, But the Season’s Over 177: He must have spotted Muriel on the way to the doniker one morning before she’d had time to get her face on.
1962		Ragen & Finston World’s Toughest Prison 797: donneker-A toilet or washroom.
1963		A.S. Fleischman Venetian Blonde (2006) 156: I excused myself and went to the donicker.
1970		(con. 1930s) E. Thompson Garden of Sand (1981) 61: He was going to be caught in a withering crossfire between stairwell and hall donicker.
1987		W.T. Vollmann You Bright and Risen Angels (1988) 313: Little evasions like when you beat the donicker* [*A con whereby two men ride a train on one ticket, one of them hiding in the W.C.].
2012		W. Keyser ‘Carny Lingo’ in http://goodmagic.com 🌐 Donniker — A rest room or toilet.