Send the bill to his parents.
Always get a lawyer to keep a record of the bill .
Sue the parents for the plumbing bill
Take the child to his parents and inform them of the damage they caused.
Charge his parents for the plumber, simple.
...slap the **** out the kid ... but doesn't reach the threshold of seriousness required you put the boot in ... but wobetide if there's a 2-peat!!!
Not a lot you can do about a kid who isn't a relative... but find out if he's related to your plumber. ;}
Is your business in New York or Boston?
Talk to his or her parents. Iowans are good in that way as a rule. ;}
Maybe she's from New York or Boston? ;} Ask her to dinner.
Even if you're positive it's him, it's your word against his. The most you can do is refuse to let him use it again. You could make the bathroom off limits except to employees. Lots of businesses do this due to problems like yours.
Place a camera outside the bathroom door so it will show who goes in and what time they entered. Each time he exits the bathroom immediately check to see if there is damage. Then take the evidence to the police. At least they might make his mom pay for the damage. And if you're lucky he will be ordered to stay away from your business.
If it happened once?
Again and again, pull them aside and tell them NO shirt, no shoes, NO FN RAGS IN MY TOILET.
Is this an employee?
How young is the kid? Why is he or she wandering around your business and flushing rags down your toilet?