Looking for Story

Long before I joined BC officially, I read a story that I've been longing to read again.

From what I remember of the story as a whole, the main character is a kid in either Middle or High School and is without his mother who "left" a few years earlier but it is found out later in the story that the abusive father had killed the mother and dumped the body in the septic system. I think at one point in the story the main character changes gender albeit I don't remember exactly how.

I hope that's enough for you guys to pinpoint which story this is.