I'm so sorry to read about dear old muffin, what a wonderful looking cat by the way, I'm not sure if will help but maybe you should concider trimming the hair around his bottom. I always put on a big jumper my cats like to be held and like to hold on when I bathe them. :) good luck for you and...
My ginger kitten will unroll all the toilet paper without putting a hole in it, so I can't tell him off, I just roll it back up and hope he finds something else to do :)