Mistress Isabella wanted to make sure everything would be the way she left it when she went away. So she did not tell her slave where she was going or how long she was staying. She just said she will be back. And before she left, she humiliated the slave a little so she could leave him with a reminder that if any of her rules is broken, there will be hell to pay.
Isabella wanted to make this slave a cocktail. She had run out of ingredients and she did not want to go to the shop to get some. She decided to improvise and come up with a great drink without too much hustle. She settled on pee. She peed into a glass and made the slave drink her pee. She had taken an expensive drink the night before so she would pass the nutrients and benefits to the slave.
Isabella was paid to punish this slave. She took him to the bathroom and pissed on his face and made him drink it all
Isabella and her slave had a disagreement. For disagreeing with her, she made him drink her pee and used him as toilet paper afterwards
Isabella wanted to degrade her slave. There was no better way for her to do it than to pee on her and watch how he reacted to it