Have you been in the middle of a lesson and a student gets up to go get some tissue? Or maybe you were soliciting answers to a question when a student asks, "Can I get some water?"
This will never happen again if you teach and model this procedure!
This one page flowchart explains how and when students in your class are to get water, blow their nose and throw away garbage. During the first week of school I teach ten procedures that help the class run smoothly.