B.H.
My grandma got custody of my brother and I when we were little and my brother was 4 and still pooping in his pants. So my very patient grandma would sit in the bathroom with him and read him books to get him to poop, if he did he got a quarter he would put in a jar. That worked for him. Prior to Grandma we were in a abusive home where he got beat with hangers for pooping in his pants and then a foster home where at 4 he had to go sleep in a crib for pooping in his pants like a baby. So Gramma's patience and love was really the thing that worked.