This is one area in which I definitely excel, so take note, friends!
This is important. Be fussy about your litter tray. If your human doesn't change it immediately after you've used it, go outside. If you can't go outside, go on the floor. It's as simple as that.
Humans clean their toilet regularly enough, so why do they expect us to put up with reeking wet gravelly stuff? After all, we have to stand in it. It's totally gross. I can assure you that the above-mentioned tactics work a treat and will ensure a pristine litter experience every time.
OK, so going on the floor will always earn you some yelling and glaring. But they get over it.
For the record, my cat litter of choice is Maxx's.