Clients often ask how often I should replace my litter boxes. We do recommend replacing litter boxes every 6 to 12 months. Litter boxes can become scratched and permeated with urine odor even though you are washing them with mild soap and hot water so it is good to change the boxes out on a regular basis.
We do recommend that the boxes are at least one and half the size of the cat. Large clear storage boxes make great cat litter boxes. If you cut a doorway in the middle of the box leaving around an inch and a half on each side to provide stability and a lip of about three and half inches to hold in the litter you can create a large box that your cat will like.