In one of my first LDs I dreamed I was taking a shower, then for some reason I realized I was dreaming and became lucid for a very short period of time, I quickly felt I needed to do something to make my lucidity worth something, so I just jumped down the drain. 
It felt like I going down a water slide! I wasn’t expecting it and the rush of the slide woke me up. But I wondered were I would come back out? What an interesting experience it would’ve been if I hadn’t woken up!
I just thought it would be nice to share this so if you wanted to you could try the Magic Water slide Drain and see were it takes you! 
Cool idea. Maybe one would come to the place in that movie. flushed. hopefully someplace more interesting though. hopefully not anywhere realistic.
I have actually once had a ND in which I went down the drain of my bath tub. I dreamed that I had learned that by going down the drain of a bath tub, you would be transported to another world. To go down the drain, I first had to fill the bathtub with water, then pull the plug on the drain and while it was draining, I would put the top of my head to the drain and turn. When I did that, I would get sucked into the drain and end up in a strange beach world.
I never tried that but if I did I would probably be attacked by some strange monster down there somewhere…