Aww, poor baby. I have a system for a relaxed and not scary cat bath. Lay a towel at the edge of the sink. Ease kitty into the water and let him hold onto the towel. It's not as scary when he has something to hold onto. Go slow. Kitty will calm down.
Yeah cats don't like water showers you can't say to him that's his punishment for sitting in the toilet because they understand what you're saying I have two cats myself and they know what you say they understand more than dogs do