On how to handle a very annoying and frustrating bit of carelessness from DD...

DD is currently responsible for making sure her bathroom is kept tidy. Toys away, clothes in the wash basket and bathtub emptied. But for some reason, she continually forgets to empty the bath. I've explained to her that before she knows it DS will start to become mobile, and leaving a bathtub full of water is not only icky but dangerous if he falls in he could drown. Essentially trying to get her into the habit of doing it now so it's less of an issue later on.

Last night she finished her bath, came out to watch some tv before bed - I asked her had she emptied the bath and she assured me she had. Only to find this morning that she hadn't. She'd lied about it. I'm at a loss for what would be the most appropriate consequence as removing toys isn't working. I need some way of drumming this into her head so she won't forget - short of writing it backwards across her forehead in permanent marker!