There was no access panel to his plumbing so I cut the wall open with a Sawzall. Since it was an old house I was not being terribly careful as I wrongly assumed there would be galvanized pipes.
Nope, I nicked the copper.
After I located the turn off valve, I opened the wall, and soldered the nick I had made.
Evidently the steam I created in the line cleared the clog, and my buddy called me a genius.
That said, I decided to to do any more repairs for him, I quit while I was ahead.