We (the humans) just finished renovating our basement, and we decided to put a cat flap on the bathroom door instead of leaving it open for access to the litterboxes, in order to keep our fresh new area fresh.
Problem is, we don't know for sure if all four kitties know to go through the flap to use the box. We know at least one does, as the box has been dirty on occasions when we've shut the door, but we're afraid at night to leave the door shut in case someone doesn't "get it" yet and makes a mess on the new carpet.
Any ideas for keeping tabs on who knows where to go? We've "encouraged" all of them to go through into the room (so we know they all fit, even Bosco here) but we can't figure a way to isolate who's doing what when we're not looking.