What do they want us to do with the bottles?

My Chinese study is paying off, though I am far from fluent. I can
understand what merchants and waiters say to me some of the time; taxi
drivers understand me. This morning, I got a student to tell me where
to find the recycling bin by waving an empty bottle at the trash can
and saying "Where are the plastic bottles?". My vocabulary is
definitely limited.

Pictures: The dining hall