Madam Tulpan had an issue with her slave and she wanted to dominate him and teach him never to mess with her again. That is why she turned him into an ass slave and she forced him to lick her asshole. She had just taken a shit when she asked him to lick her ass. One look at him and he knew that she would never let him get away with not licking it so he did.
Madam Tulpan wanted to get her ass licked by this loser and she did not want any negotiations about it. There was no backing out of it and she made sure that she had a great time torturing the slave as he was forced to lick her ass as well as her asshole, which was not very clean at the time he was ordered by the mistress to lick it.