I use plain old ground-clay litter: the stuff that comes in
50 lb bags at the pet supply store.  (The bags are getting
heavier every year!)  My herd (4) share four litterboxes
(plastic dishpans) and this works fine.

Every second day, I scoop out the poop and then carefully pour
the litter from one box to another - transferring only the dry
stuff.  I scrape out and discard the wet litter, rinse the box,
sprinkle the bottom with a little baking soda and refill with
the litter saved.

Roby

I also am using an Omega litter box and I've had reasonably good luck with
Arm & Hammer Easy Flush which, as the name suggests, can be flushed down the
toilet. Once a day (sometimes twice) I roll the box and collect the solid
matter in the scoop. I can go a month just topping up the litter and then I
disassemble and thoroughly clean the box. My single cat does poop in one end
of the box and pee in the other. My cat is a large Maine Coon. With three
cats you will likely have to more frequently roll and empty.