All these homemade exhausts look ok and may do the job. My concern would be if I or someone in the area got CO poisoning. There is always going to be someone wanting to go to court and sue someone. Although its no guarantee I would rather try a defense based on an exhaust designed for that purpose rather than some materials from the hardware store being re-purposed as an exhaust. Maybe I am paranoid but I am a product of my environment living in Florida everyone seems to sue thy neighbor for what you can get.