Green’s Dictionary of Slang

poo v.

also pooh
[poo n.1 (2)]

to defecate.

[UK]C. James in Observer 6 July 23/1: The dog practically has to poo on his shoe before he can make the pinch.
[Can]M. Atwood Cat’s Eye (1989) 245: She is referring to her dog Spot, who has poo’ed on the carpet.
[UK]K. Lette Foetal Attraction (1994) 145: It’s trying to train a two-year-old with diarrhoea to poo in the potty.
[UK]N. Barlay Crumple Zone 102: Jake’d make Norwich Union poo in their premium-padded pants.