N.B.
Please stop punishing him. It doesn't work anyway. Have a talk with him, and tell him that you will no longer be cleaning up after him. From now on, it will be his job to take off his poopy pants, clean himself and his pants, put them in the hamper, and put on clean underpants. No scolding, no punishment, no drama. Stand over him to supervise, but make him do all the work. Right now, he's winning the battle. Stop fighting him, and make it his decision to use the toilet. That's what he wants.