I have three cats and two litter boxes (one box is standard sized the other is bigger than normal, 15" x 21"). I have heard that it is a good idea to have one more litter box than cats but when I had an extra one they didn't use it. At any rate I have been using precious cat (clumping clay litter)- costs about $10 for 40 pounds. Is it better to pour in a thinner layer of litter and completely empty the litter out every week, or use a thicker layer of litter and completely change it less frequently (every 3 weeks)? I try to scoop every day but sometimes its every other day. Thanks for any advice.