Short answer
Drums, rakes and open-tops need clumping litter; most are designed around clay and many reject pellets. 17 boxes here list tofu as compatible and 13 rule it out. Crystal-tray and flushing boxes take only their maker's own consumable.
A sifting box separates waste by size. Urine has to bind the litter into a clump bigger than the holes in the screen, and it has to hold together while the drum turns. Litter that absorbs without clumping passes straight through the screen with the urine in it, and loosely clumping litter breaks apart and smears.
That is why non-clumping, paper and large wood pellets are on almost every do-not-use list. Whisker adds plant-based litters to its list, asks for standard-weight clay, and rules out translucent or white litter on most models.
Tofu litter clumps and is popular for being flushable and light, but the pellets are long. Makers that accept it usually give a size limit: PETKIT allows particles up to 12 mm long and 3 mm across, Meowant under about 15 mm, and CATLINK's Pro-X family excludes long-strip tofu. Oneisall sells a coarser 12 mm guard for tofu and mixed litters.
PetSnowy's SNOW+ has the widest published list, naming clay, silica crystal, tofu and clumping pine. Whisker's Litter-Robot 5 accepts silica crystal as long as it passes the screen, while its other models list translucent litter as unsuitable.
Crystal-tray boxes run only on their maker's tray; the tray is the litter. CatGenie's A.I. runs only on its washable granules, and the Whoosh only on CatGenie's soybean-pulp flushable litter, with ordinary litter voiding the warranty. Casa Leo goes further in the other direction for a drum: its Leo's Loo Too warranty covers 100% clay clumping litter only.
Rotating drum
Best for: Owners who use pine, tofu or crystal and do not want to switch
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Rotating drum
Best for: One or two cats under 22 lb, especially older cats that struggle with a high step
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Flushing
Best for: Two or three cats in a home with a drain nearby, where nobody wants a waste drawer
Check price on AmazonEvery automatic box waits until a sensor says the cat has left, then separates clumped waste from clean litter and puts it somewhere sealed. Drums turn the whole chamber over a screen; open-tops do it under an open rim; rakes comb a flat bed; crystal-tray boxes rake a disposable tray; flushing boxes wash waste down a drain. The mechanism decides which litter you can use and whether you buy a consumable every month.
Less than with a normal box, but not nothing. Empty the drawer, top up litter as the level drops, change carbon filters or deodorisers every few weeks, and take the box apart for a full clean every one to three months. The makers' own intervals are below.
Every specification explained, with the real numbers from the catalog behind each one.