How to get your cat to give himself a bath in the tub

Mr. Binx comes into the bathroom the second I run the water for the shower. He sits and waits for me to finish and the second I turn the water off he meows and jumps into the tub. After a few minutes of tub licking comes bath time in the tub. It's really quite convenient when your cat does his own bath time and cleans your tub for you.