I've got a finished bathroom that failed an air test. I need to find the leak(s) and repair it(them). I understand that this will involve cutting into some walls/ceilings. I had a plumber come out to give me a quote. He said they would have to re-plumb the entire drain and vent system. I'm not sure if everything is up to code since I had a friend who used to be a plumber (and is not licensed) do the plumbing. Is it really necessary to redo the entire system? If so, what's a fair price range? I realize no-one can give an accurate price without seeing it, but how about a range? The quote I got was $8,000. When I originally started the bathroom I got a quote of $4,500 to rough-in the entire system, including water supply lines. That's looking pretty good right now. Lesson learned.