Green’s Dictionary of Slang

an act of defecation.

2000		personal correspondence: Donald Trump – Modern Rhyming Slang for ‘dump’ (defecate). e.g. ‘I’m just nipping out for a Donald’.
2005		P. Howard Curious Incident of the Dog in the Nightdress 270: Looking like someone’s taken a focking Donald Trump in one of his Dubes.