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*
That was actually answered by Pottermore (I think? Somewhere official)- the castle adapts itself to modern technology as it sees fit. There might have been washrooms, tunnels, holes in the foundation, etc. that were originally intended for the basilisk to travel through, and when the need for indoor plumbing came, the castle adapted itself and turned whatever was there into plumbing and sinks and toilets.
SO HOGWARTS MIGHT HAVE WIFI?