How Do We Keep Our Toddler From Keeping His Hands Out of the Toilet?

• Isaak has a new hobby; he tries to plug the little hole in the bowl where water comes out to fill up the toilet. 
• He wants to be a plumber when he grows up. What can I say?
• Last night I discovered this new hobby. I got after him.
• Tonight Daddy caught him in the act of doing the same thing tonight. 
• Daddy startled Isaak big time! He cried. 
• I'm hoping this hobby has ran it's course.