Well, you have certanily worked hard at describing symptoms and diagnosing. KimOriginally Posted by Kim
Was your plumber a Master Plumber?
To me, this is an interesting challenge, to work with you to figure it out. The part I quoted above is the where I would spend my time, if I were to come over and start poking around.
Who was the plumber thast the previous owners used? What does the original builder say? Were other houses build by him at the same time? Sooner or later you will get another idea, or one of your previous fixes will be re-done differently... i hope.
My unprofessional opinion.