which story?

My partner and I read a story a while back and were hoping someone will know which one it is and the title etc!

It starts with a girl joining a slave ring where the girls are bid for by men on a weekly basis and go to the highest bidder, her first experience is of a meal where the slaves are used as lights and serving dishes, she is made to pee in another girls mouth, and the girls get her back at one point.

One girl decides to leave with her master and be brought by her but it means she has to be branded by each of the slaves/masters in turn

Anyone got any idea? Searched nearly 2000 of the stories already!