The litter box is not a storage container for poop (or anything else that comes out of a cat).
The litter box is, rather, a place for cats to deposit their, er, business. After which said business should be removed in a timely manner. NOT allowed to accumulate until it becomes disgusting.
The fact of the matter is that a properly maintained litter box will not smell any more than a regularly flushed human toilet will. Which means it's best to scoop at least twice a day, and that if you have multiple cats, you should have multiple litter boxes.
I admit I've become a bit of a zealot about this, but only because I know how many cats are given up to shelters and subsequently killed due to "litter box issues". When in reality, I'm sure that many of those "issues" were probably either medical problems (undiagnosed UTIs, etc.) or matters of protest due to improper box maintenance.
That said, I realize sometimes people have problems cleaning the box due to illness, disability, etc. And if the box isn't getting cleaned in that sort of a situation, it's due to the cat's human not receiving adequate support. Which of course is a problem in and of itself. This post is NOT meant to denigrate anyone who cannot scoop litter themselves -- again, if you can't scoop, you should absolutely be getting assistance from someone who can -- but rather, to note a few things that might help whoever is supposed to be cleaning the box do it more often.
And it just occurred to me tonight that perhaps part of the reason litterboxen often get neglected far longer than is right or healthy is because too many people think of the box as a kind of....poop reservoir, or something, where basically you only clean it out when it fills up completely.
I've also met a number of people who believe that catboxes "just smell" and that this is normal/acceptable/okay. Even when their cats are suffering from ear ulcers due to having to enter a covered box reeking of ammonia fumes I've seen people baffled that I think something is wrong. And so I figured something like this post was in order.
In the interest of full disclosure, I should acknowledge that I am myself a reformed catbox-neglecter. When I was younger, I would basically wait until my parents nagged me to clean the box -- the consequence of which was that my poor cat Tim ended up with a box so nasty he eventually got fed up and decided to use my acid-washed-denim-look-neon-paint-splattered beanbag chair instead (seriously, I was all about to sit down and play Zelda one day when I was around thirteen, and very nearly sat in the middle of a tidy pile of feline feces!).
After that I got a little better about scooping, but it wasn't until I was an adult, with 4 cats of my own, that I figured out the actual meaning of litterbox cleanliness. And I am so glad I did figure it out because, well, my house doesn't stink, and my cats are so happy with their bathroom facilities that they use them regularly and perfectly. And I would never dream of going back to my preteen method of "wait until something bad happens, then clean the box". It's much, much more pleasant for everyone when the box is treated as a temporary waystation for waste as opposed to an accumulatorium (if that's even a real word) for same.