You have two round muscles in your rectum, the outer muscle and the inner muscle. If both are properly trained, you can get incredible depth during your sessions. If you only work on the outer one, you will only get good width. But if your assmaster is wanna do almost daily fistings, your gonna want to condition the inner ring muscle too, so you can give him the most of your rectum for fistings. The rectum is mearly the cavity between the two ringed muscles. Your gonna want to expand the cavity alot too, so you can accept the biggest fateest toys into your rectum for him.
So you need to work all three to achieve your goal:outer ring, inner ring and rectum:
OUTER RING MUSCLE Technique-The outer ring muscle can be 'busted' by using your biggest dildo you can take. It must have a nice distinct head. Have him punch fuck that monster over and over as much as you can take. Do this DAILY or as much as you can. These punches should be deep insertions and complete pull outs every time to abuse the assmuscle. This will also expand your cavity, since your getting filled with air too.