Ok, my ducks have a house they're locked into at night with a large wire box attached to the front so that they can sleep outside if they wish and still be safe. The problem is because we have a variety of ages we have to keep water available all the time, so we put a 5 gallon waterer in the box as well. This makes for one ucky box floor. I'd like to do something for a filtration system, simple, but effective. my husband has an idea of gravel then sand over it, but I would think that the sand would just pack in the gravel and get ucky as well. What do you guys do? Any ideas?