Green’s Dictionary of Slang

dunnaken n.

also donneken, donnykin, dunegan, dunnakin, dunnekien, dunnick, dunnigan, dunnikan, dunniken, dunnyken, dunyken
[danna n. + ken n.1 (1); note synon. US carnival use donniker]

1. [late 18C–19C] a lavatory; also attrib.

2. [1960s] as a term of abuse.

In compounds

dunnigan (worker) (n.) (also donegan worker) [worker n.1 (1)]

[1930s] (US Und.) a thief who hangs around public lavatories, hoping to steal from discarded coats or take parcels etc. that have been put down.