For a jazz piece I am learning to play, my camp teacher wants me to use a plunger mute, does the bottom of a regular plunger (red part) work for it, and do I need to to anything once I take it off the stick if so?

<Added>

Or do I need to buy one at a store, just making sure?

Yup, just a regular old plunger. Preferably not used, of course.

You can go to the music store and spend $15-$20 on the same thing you can get at the harhware store for $2, but why?

Yeah, I play trombone more then my trumpet, sorry if I sounded saying that, if I did I didn't mean it.

<Added>

*if I sounded MEAN when I was saying that...*