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.