I've discovered that when it comes time to "flush their toilets" each night, wherever I am becomes the most interesting place in the apartment to be.
As soon as they see the trash bag and bin of fresh litter, they come running and start trying to "help" me in my task. Said help usually consists of jumping into their previously forgotten litter box and staring at me or jumping into and out of it spraying bunny funk all over their cage in excitement.
Once they've been chased out of the litter box, River generally makes a habit of trying to suffocate herself in the trash bag. At least this time she isn't fighting me by trying to climb into the bag while I'm dumping the manky litter. You laugh, but it has happened before! She seems to not understand (or care) that this is the opposite of being helpful.