Well I have 2 Flemish Giants, only about 9 weeks old, but only one litter box, so I change it every day. They are constantly going to the bathroom. They are pretty good about using their litter box, when I was cleaning it out I had just emptied it and was going to get some fresh litter and Firefly hopped in it and used it without the litter anyway. The pet store that I got them from had litter boxes that didn't use litter. They were like those corner boxes but with a grate on them. I'm tempted to try those to save on litter, but I don't know if I could find one big enough for 2 full grown Flemish Giants.