I am aware of the need to vent a sewer pipe but I have heard that there is a requirement to add additional vents if the pipe gets too long. I am using a 4 inch PVC for the sewer pipe and have a 3 inch vent pipe planned. The sewer pipe will travel about 35 - 40 feet before connecting to the existing septic line. I know that code requirements are local, but I am looking for a general need that will ensure proper drainage. I would appreciate your comments.