Thought I'd pop in really quickly with a little anecdote from last night.
Our bath time routine is what everyone else's is, I'm sure: get in, play, wash, put the toys away, open the drain in the tub, get out. At the end of Ivy's bath last night, I had her hand me her toys one by one. When the toys were cleaned up, she turned and pointed at the drain plug. Yes, baby, that's what comes next! Good job!