I made a sandbox for my chickens, outside the coop, with play sand, and added a bunch of diatomaceous earth to it. They really like to get in there and dig down and fluff the mixture into their feathers and the DE may help with external parasites, though I haven't had any problems with that, so can't say for sure. Yes, they poop in it, not very much. I just clean it out occasionally (like once every few months) with a small manure fork. Mine is just an old wood frame - I think it was part of an old bookshelf, laid flat directly on the ground. I don't see why a rubbermaid container wouldn't work, though it wouldn't drain if it got a lot of rain in it, so you might want drain holes in the bottom. They WILL dig down into any dirt or sand you have in the run and create their own dustbath if you don't supply one, if they are on dirt, rather than wire or whatever.
