Hogwarts also has modern plumbing, which was presumably not put in by hand considering whoever did it would've found the chamber of secrets in that one place they put a bathroom. I think we can safely assume it will grow new features.
The magic level of the Chamber is sufficiently high that one could conceive of it using an equivalent of a high level Confundus charm on people so that they could install plumbing and yet not notice. But you have a good point and your explanation sounds simpler.
Update: Discussion has moved on to a new thread.
The hiatus is over with today's publication of chapter 73, and the previous thread is approaching the 500-comment threshold, so let's start a new Harry Potter and the Methods of Rationality discussion thread. This is the place to discuss Eliezer Yudkowsky's Harry Potter fanfic and anything related to it.
The first 5 discussion threads are on the main page under the harry_potter tag. Threads 6 and on (including this one) are in the discussion section using its separate tag system. Also: one, two, three, four, five, six, seven. The fanfiction.net author page is the central location for information about updates and links to HPMOR-related goodies, and AdeleneDawner has kept an archive of Author's Notes.
As a reminder, it's often useful to start your comment by indicating which chapter you are commenting on.
Spoiler Warning: this thread is full of spoilers. With few exceptions, spoilers for MOR and canon are fair game to post, without warning or rot13. More specifically: