Lavatory

• Type: Public Facility, Restroom
• Location: Various, notably within Hogwarts School of Witchcraft and Wizardry and the Ministry of Magic.
• Owner/Residents: Varies by location. The ghost Moaning Myrtle is a permanent resident of a specific girls' lavatory at Hogwarts.
• Key Features: Wizarding lavatories are often similar to their Muggle counterparts but can possess unique magical properties, including serving as enchanted entrances to other locations, being haunted, or containing secret passages.

A lavatory, also known as a bathroom or toilet, is a common facility found throughout the wizarding world. While functionally similar to Muggle lavatories, they are often sites of significant magical activity. At Hogwarts, the introduction of a more elaborate plumbing system in the eighteenth century was a notable development. Before this, wizards were less concerned with sanitation and simply used magic to vanish their waste. The new plumbing was installed, in part, to be more discreet around Muggle observers of the castle. This modernization had a significant, unintended consequence: a descendant of Salazar Slytherin, Corvus Gaunt, took advantage of the construction to incorporate the hidden entrance to the Chamber of Secrets into the pipework of a new girls' lavatory. (Pottermore) Lavatories within the wizarding world can be enchanted for various purposes. The entrance to the Ministry of Magic for most employees involves flushing oneself down a toilet in a public lavatory in London, and the Prefects' Lavatory at Hogwarts features an enchanted, swimming pool-sized bathtub.

Despite their mundane function, lavatories serve as the backdrop for several pivotal events in the series. In their first year, Harry Potter, Ron Weasley, and Hermione Granger battle a Mountain Troll in a girls' lavatory, an event that solidifies their friendship. In their second year, the same lavatory becomes their base for brewing the Polyjuice Potion in an attempt to uncover the Heir of Slytherin. This lavatory is also the location of the secret entrance to the Chamber of Secrets. In Harry's sixth year, he and Draco Malfoy engage in a violent duel in this lavatory, which culminates in Harry grievously injuring Malfoy with the Sectumsempra curse. Albus Dumbledore also mentions that he first discovered the Room of Requirement one morning when he was in desperate need of a lavatory, and the room appeared for him filled with a collection of chamber pots. The lavatories at the Ministry of Magic serve as a clandestine entrance, which the trio uses during their infiltration of the Ministry in their search for Salazar Slytherin's Locket.

• Moaning Myrtle's Lavatory: A girls' lavatory on the second floor of Hogwarts that has been “out of order” for years. It is haunted by the ghost of Moaning Myrtle, a student who was killed there by the Basilisk. One of the sinks features a tiny, scratched snake on the tap, which marks the entrance to the Chamber of Secrets; the entrance opens when one speaks Parseltongue to it. This is where Hermione Granger hid from her classmates on Hallowe'en in her first year, leading to the troll attack. It was later used by the trio to brew Polyjuice Potion.
• Prefects' Lavatory: Located on the fifth floor of Hogwarts, behind a door whose password is “Pine-fresh.” This luxurious bathroom is reserved for school Prefects and Quidditch captains. It features a large, rectangular, swimming-pool-sized marble bath with hundreds of jewel-encrusted taps that dispense water mixed with different types of magical bubbles. A large painting of a mermaid on the wall is a key feature. Harry Potter used this lavatory to decipher the clue of the Golden Egg for the Triwizard Tournament's second task, with help from Moaning Myrtle.
• Ministry of Magic Lavatories: A set of public toilets on the surface in London that serve as a secret entrance to the Ministry of Magic. Wizards and witches enter a toilet cubicle and flush themselves to be transported into the Atrium of the Ministry. The trio used this entrance after stunning Ministry employees Mafalda Hopkirk and Reg Cattermole.

• According to J.K. Rowling, the decision to place the entrance to the Chamber of Secrets in a bathroom was partly to mock the idea of a grand, obvious entrance for a secret chamber. The idea of plumbing being a later addition to the ancient castle of Hogwarts also provided a logical explanation for how the entrance could have been concealed for so long. (Pottermore)
• In the film adaptation of Harry Potter and the Chamber of Secrets, the girls' lavatory is explicitly located on the second floor, which aligns with evidence from the novel. The set design for the Chamber of Secrets entrance, with the ring of snake-engraved sinks, is a memorable creation for the film. (film)