Bodily autonomy

My daughter is 6 years old and very autonomous. She spends at most one day a week at her dad’s and she resists going to see him, though I try to encourage their relationship as much as I can. Her dad has this thing about when she goes poop that he has to wash her butt in the bathtub otherwise she isn’t clean. I think this is really too much, though when she was little I didn’t say anything about it because she didn’t care. But now she is telling him she doesn’t want him to do that and she cleans herself really well, like she isn’t a kid to leave herself with a dirty butt and she bathed every night. Today she came home saying she told him she doesn’t want to and she’s not a baby anymore but he insisted and washed her. I don’t even wash her butt anymore, like she’s 6 and it’s her body. I feel he’s violating her bodily autonomy. I intend to talk to him about this but I wanted to take the pulse on this kind of issue for a kid her age and see what you all think.