Well, Muffy seems to have completey forgotten how to use a litterbox!
I cleaned the box, washed it out and put new litter in it. She's still using the tub. She stopped hissing and growling, however.
I'll be getting a different litter type this weekend, so I'll let her remain in isolation and put the new litter in her box then and see what happens. The tub is easy to clean out in the meanwhile. Hey! It's better than carpet or my bed!!! Besides, until I know for sure that she's litter trained, she stays in isolation.
I'm just like any other cat owner - I hate the smell of cat urine and I don't like cats to be going where ever they feel like it.
It's hard on the others, though, because this cut them from 3 boxes to 2. I'll need to get another litter box so that I have enough for the 6 cats. With one cat dominating a litter box, it makes it very important to clean the litter boxes regularly - not a problem in my case, but just a general observation.
In any case, 2 boxes for 5 cats (the cats with free run of the house), that's not enough boxes. I try to keep at least 1 box for 2 cats, so I had 3 in use - now Muffy is dominating the 3rd box. Bugs will use the furniture if she can't get to a box whenever she needs to. That stinks! So, I need another litter box.
I don't know if this is making any sense, but it does to me.