i have two kitties, and they have two litter boxes (i believe the ratio is 1 kitty: 1 litter box?)
i scoop out their undesirable about 3 times a day, sometimes more, as they have a tendency to use the litter boxes IMMEDIATELY after i empty them.
i like using metal scoops as they do not absorb odor.
i wash their litter boxes/mats/litter covers once a week.
Yesterday, i just did the task. i put on a pair of gloves, then wash the litter boxes/mats/covers with extremely hot water and detergent. i scrub with a brush especially for such purposes. After washing them, i would wipe them dry with paper towels, and blow dry everything.
Lastly, i refill with new litter. This way, there is no opportunity for "funny odor" to arise.
Laurie has her own (she is in a large crate waiting to be spayed)
ashton has his own (he is in his own room waiting to be neutared!)
Grant and Marble share a box
Blizzy, nimby, stormy and snowwhite share two LARGE litter boxes
Moe and Neo each have there own box.
Once the kittens are running around the house and the ferals are back outside I plan to have 4 or 5 litter boxes in the house.
I scoop moe and neo's everyday or every day and half.