So I am having my roof replaced next week and need to run a new stack vent for, my main house drain, through the roof. The stack is 3" PVC but Ive been unable to find a vent stack flashing that will accomodate a 3" PVC pipe. The folks doing my roof are a major company and do plenty of roofing in my area. Am I safe to assume they will have a way to make this work or do I have such an odd sized vent size they need to special order something. Thanks everyone!