Green’s Dictionary of Slang

growler n.4

[the noise, either of someone straining to defecate or of incarcerated prisoners]

1. a lavatory, usu. in a prison cell.

[US]Berrey & Van den Bark Amer. Thes. Sl.
[US]Monteleone Criminal Sl. (rev. edn) 108: growler A chamber pot used in a cell.
[US]G. Underwood ‘Razorback Sl.’ in AS L:1/2 60: growlern Toilet.

2. a prison.

[US]R. Graziano Somebody Down Here Likes Me, Too 136: The police take ’im in for a night in the growler.