Thanks for the tips! We've tried different types of clumping clay litter, scented and unscented. Right now we're trying out the Arm and Hammer natural clumping litter because it's easier on the cats' digestive tracts. I haven't seen the Cat Attract litter before but will be on the hunt for it!
Stan (you're right!) is about 11 lbs. I believe the vet called him "chunky". I don't think he looks really overweight, he has a habit of curling up into a Popple position which makes him pretty tiny. Both of our cats eat MediCal Dental food from the vet. We don't usually give them wet food because the other cat, Molly, has a pretty sensitive stomach and barfs a lot. When I've given Molly the hypo-allergenic wet food from the vet in her diet before, she usually spends the next couple of days barfing and suffering from diarrhea. We usually leave food in their bowls all day long because if we don't, Molly will over eat at meal time and then will blow her entire dinner. I can try giving just Stanley some wet food though - let's hope Molly doesn't get too jealous! I will also pick up one of those under the bed storage bins. We have two regular sized litter boxes and one large one - it's the largest I've ever seen that's still a litter box. But maybe if we get a storage bin, we can get rid of the two smaller boxes.
I'll try this stuff out and see how things go over the next week.