Researching sanitation today, I ran into toilet ghosts.
You know Moaning Myrtle (Shirley Henderson, in the films), from Harry Potter. [source]
I can't find any evidence, but she seems to be a version of Hanako, a Japanese ghost who has hung out in school bathrooms since the 1950s. Hanako appears when you call for her. Mostly harmless, in most versions...
Art by cute or death.
This idea that you would willingly call for a ghost (why?!) reminds me of a tale I heard at sleep-overs:
Look in the mirror and say I believe in Mary Worth three times, and she will appear.
For years, I was scared to go to the bathroom at night for fear I'd accidentally call her up since it was impossible to glance at the mirror without thinking the phrase.
[reading up on it, the more usual name is Bloody Mary.]
I can't remember what Mary Worth was supposed to do to you, but I do remember being baffled by the existence of a comic strip about a nice older lady named Mary Worth:
P.S. I found a blog Mary Worth and Me that "celebrates how hilarious it is."