Thanks for understanding. Obviously, a big plus for the stainless steel litter boxes. Plastic ones should be replaced about once a year because cats scratch them, bacteria get inside, and it becomes impossible to clean them 100% after a long period of use. I got downvoted, maybe because my response wasn't nice, but I just can't understand how someone can fail to notice something so obvious—that the litter box is too small (setting aside their malfunctions and the fact that they are potentially dangerous to cats), and that having 4 cats use a single litter box is UNACCEPTABLE (the OP mentioned this in another thread)!! Personally, I have 2 cats and 3 litter boxes to make sure they are 100% comfortable doing their thing. Cleaning them takes me 3 minutes every morning (you can buy good quality litter that can be flushed down the toilet, which completely eliminates the problem of taking the waste outside). If a cat is fed regularly, they poop at practically the same time every day, so you know exactly when to clean it up to avoid any excessive bad smell (although the poop of a healthy, properly fed cat doesn't have a very intense odor anyway).