I use "All Natural Unscented Scoopable Cat Litter. I've learned a new trick after trying to scrape the equivalent of cement from the bottom of your box. What a pain. Especially when it's still wet and sticks to the scoop.
Helpful hint:
After thorough bleaching both the box and scoop and drying them, spray the inside bottom of the box and the scoop with PAM (vegetable spray). It prevents the litter from sticking on either.
:D:D:D:D