In the scene where Will drowns you can clearly see that before the water starts coming up that the plug isn't plugging up the sink. He had no reason to reach into the water to unplug it when it was never plugged up to begin with
Quote of the Day-
Dean: Alright, if you're gonna be talking now, this is a very important phrase, so I want you to repeat it one more time.
Lucas: Zeppelin rules!