Jojo

Good morning everyone, I really need your advice. I am going to build a sauna with a toilet and shower block behind my garage. I am going to connect a drain pipe into my house's sewer pipe, y using a T section. Question is: do I need a permission from inspector or south water, what is the right way to do it without getting a fine? I have received an answer from council that application is not required for my building, but what about the waste pipe connection. Thank you for your time