NOTE for best results, you can combine pranks. if you dont know the first one, here is a link to the original toilet prank
Step 1: Turn Off the Water
Step 2: Now... Flush!
Step 3: Enjoy!
as i said on the intro, this will give you 4 times the laughs when you use it in conjunction with the other toilet prank i posted
again, a picture for this kind of instructable is inappropriate and would violate the terms of service