LOL. Mine sit in wait and as soon as I'm done they each are in one!
As I can't smell (sometimes a blessing) and apparently lax in my regular cleanings, my little Clio let's me know when it's due for a cleaning by poping in and out of the hallway looking at me and mewwing. She's done this for years and it still gives me a chuckle.
Sporticus takes somewhat of a tantrum and starts digging loudly.