My 2 cents:
Since he's made this a power struggle between you and him.... turn it around and ask him what it will take for him to clean up his act. He'll probably say..."I don't know". Well then give him 24hrs to come up with a plan to fix the stinky situation and have him pick a reward if he follows through on his plan. Yes, you are going to bribe him. (The reward will need to be agreed to by all parties involved. Maybe a game, money, more screen time, etc.). Treat it almost like a business. Wouldn't hurt to type up the main points and everyone signs so there is no confusion.... This also sends the message that it's a real problem and you are not just nitpicking at him.