Mistress Madison needed to make this guy drink pee and that is exactly what she had him do. He did not see it coming and he did not expect it but it was what he was supposed to do and he had no choice but to do it. Shew as going to make it worse for him if he did not make any changes and so he had no alternative but to do it.
Mistress Julia did not want to physically hurt anyone. But she knew she had to give a cruel punishment. The kind of punishment that is not easily forgotten. That is why the mistress turned to pee and she used it to achieve what she wanted. It was easy for her as the slave was not prepared for what she was about to do and what she eventually did to him.