Movie about 2 teachers in a boarding school killing the principal but he is not really dead

I am looking for the movie about 2 female teachers in a boarding school killing the principal but he is not really dead, I remember a scene where they are wrapping him into plastic sheet near a bathtub.
Also there was a boy from the school unclogging the pool and everybody was watching in tension what the reason was for the pool being clogged.

I also remember that the principal came back to take revenge and I also remember a woman appearing because she was pregnant and she was looking for the principal to ask him money, but the 2 teachers blew her off with a cheque and so she walked away without asking too many questions.

I think the movie is from the late 90’s but I could be wrong.

I cant really remember anything else from this movie and I am hoping someone knows this movie because I would really want to watch it again

Thank you