I heard a pretty nasty 121 story from one of the guys in my ground school. He was the captain on a 737 in India and said that the ground crew could not get the drain valve for the lav to open. He went back to take a look at it with some tools.
He ended up getting a nice spray shower of all the contents in the tank. He found a shower somewhere and changed clothes because he still had to fly in an hour or two.