Mistress Nica used her pee and her shit to punish her slave and she made him regret what he had done to her. She was disappointed in him and that is why she made sure that he learned his lesson the hard way by making him a toilet slave. The poor guy had to drink pee and also eat shit. None of those things was negotiable. He had to do them all.
Mistress Nica and her friend wanted to humiliate this guy because he was a nuisance. They went ahead to caution him that they would not tolerate him continuing his nonsense and so they gave him a last warning. He did not adhere to it and had to be punished as a result. That is how he found himself eating their shit and drinking their pee. He never repeated his mistake after that.