Keeping the class clean

I am in the midst of looking for a gym, and am suprises how often the topic of cleanliness comes up! It is really important to some people to have a clean place to workout. Similarly, I think classrooms should be kept tidy. Nothing wrong with chaos while the lesson in happening, but it shouldn't have pointless trash left about after class.

Since I have my students every other day for an hour and a half, it is kind of hard to establish a routine. I'm not sure if what I've seen other teachers do would work for me, but I hope I can get some comments on different ways that teachers motivate students to keep class clean.

I can remember a lot of my teachers doing different things

I remember one of my teachers who actually had a rule that in order to leave the class we had to give her a small handful of trash. However, I also remember storing pencil shavings for just this purpose!

Last fall I had to forbid a class from taking their water bottles out of their bags. They had repeatedly left them behind after class and reminders didn't work. They improved a bit in Spring, but I still find myself repeatedly reminding people to pick up their trash. I wouldn't mind it, except sometimes I am circulating and teaching and I don't get a chance to remind them.

I recently decided to set up a little basketball hoop over the trashcan which I found worked well, except some students spend more time creating trash to throw away rather than work on their groupwork (these are the same students who proclaim they don't have enough time to finish activities in class.

How do YOU keep YOUR class clean?Positive reinforcement? Monster shaped trash can? "Clean" row leaves first?