I'm ALWAYS on the prowl for bargains, so this does sound like a good idea. The only thing I would say is that you will want to make sure that you permanently label those plastics so you do not use them for something else. If you are talking about the Rubbermaid© type containers...they are notorious for holding scents in the plastic.

Tony's idea of cat litterboxes is actually an excellent choice since they are made to withstand ther permeation of odors.