Sue
I have 4 cats with 2 litter boxes "going" at all times and I have 2 spares.
I switch them out every couple of months with clean ones. I soak the "dirty" ones in the basement washtubs with dish soap, a little vinegar and a few drops of bleach. I dry them outside in the sunshine and then they're ready for next time.
Only cat lovers know the luxury of fur-coated, musical hot water bottles that never go cold." - Susanne Millen