wait
hogwarts was established in the 10th century
but sinks were not invented until the 18th century
so how did salazar slytherin mark the chamber of secrets with a form of indoor plumbing which would not be invented for another 800 years
?????
*looks for historical inconsistencies in a book about wizards*
Perhaps the room was enchanted like the room of requirement and the door to the chamber disguised itself based on the way hogwarts changed. I mean, the door would be much more obvious if it was a fountain in a random room rather than a sink in a bathroom.