[Dionysus]

This would work both as a way of training a slave in anal, as well as a useful and degrading punishment:

Have your slave push a condom into their ass so that a little still sticks out. then, every half hour, or as regularly as you want, have them then put a marble or other small object into the condom, keep adding for as long as you want your slave to.

his is particularly effective for a day long task, and it can be changed as you want depending on what you want your slave to do.
let me know what you think.