Heres something interesting to note. When Irwin is confined to a bathroom, he gets a food bowl, water dish and his own cat litter. He will not spray "his" bathroom. There is always urine in the litter.

Does this mean that he isnt spraying because its already "his" room?

I have plenty of cat litters in the rest of the home, Ive seen him walk right by to spray a wall. But the rest of the home is "shared" with the other cats.