I use regular litter boxes and clumping litter. I have always liked the clumping litter because it is easy to clean and it keeps the smell to the nonexistent point. What's funny is that Ming is a very large cat, over 20 pounds (his nickname is Waddles). Mac is on the small side, around 7 pounds. Neither of them has a problem fitting into the box in the kitchen, no litter is scattered and they never "thinks outside the box". In my son's room, we have a different story altogether. The litter is scattered everywhere. I put down an old bed sheet and they still kick litter outside of that. Plus, I find tootsie rolls on the sheet all the time. Go figure.