R.I.
OMG this was me. My son not quite as old but he was completely potty trained when it came to peeing in the potty and even at night he was potty trained but if he didn't want to stop what he was doing he would poop on himself. So I took my best friends moms advice. I stripped him down. I let him run around the house naked. He pooped on the floor 1 time. When he did that we made him clean it up (which he thought was disgusting) and then after that he had to get straight in the bath tube clean himself and get right out. He was not happy about not getting to play in the tub. But like I said he did it once. It took a little while of letting him run around the house naked and when we went out or had company he we had to put clothes on him and watch him closely but that is it.
Also my sister lived with me while she was potty training her son and I did the samething with him. Lucky enough he never used the bathroom on the floor he always ran to the bathroom. But I never had to worry about dirty clothes with him. This method works I know it may be gross sometimes but it works.