I have been told by a plumber that all the sanitary tees in my house are installed backwards. Also that the sanitary tee can not be installed on its back for sewage drain. What is considered the BACK of a sanitary tee?
Thanks,
Confussed in San Angelo

Here you go, happens to be the code question of the week so read up. https://ibcode.com/uploads/Aug_24_Sanitary_Tee.pdf