John Doe wrote:
The local megastore is selling Sterilite 70 and 90 quart "EZ Carry" boxes,
the kind with the milky clear smooth sides. Never needs cleaning. Probably
there sturdiest plastic boxes. Including handles for easy manipulation. The
70 quart model might be best for most situations. Only used for about a
week, but if my experience with their other boxes holds true, this sturdy
version is an outstanding litter box.

My understanding of litter box:
It's bad if it has a strong smell of plastic. An old box may be better
than a new one, because it doesn't smell like plastic anymore.
It should be wide enough for the cat.
The cat thinks of it as his if it smells of his **** faintly; if it
smells full, he won't use it. So clean it and rinse it, but don't work
to completely deodorize it.
If there are two cats, there are two possible behavior responses. He
may not want to use the box with the other cat's scent in it, which is
bad for you; or he may feel driven to overwhelm the other cat's scent
with his own turds and urine, which is what you want.
If the cat kicks litter all over the place or scratches the wall beside
the litterbox, you can get a deep plastic storage container and saw a
cat-sized hole in the side of it 2 inches from the bottom.