• In this video, This Old House general contractor Tom Silva shows how to create a watertight seal around a vent pipe.

    1. Use a pocketknife to scrape rough edges and sharp points from upper end of plastic vent pipe.
    2. Cut away the old caulk from around the vent pipe. Use the knife blade to scrape the pipe clean and smooth.
    3. Apply a thick bead of lap-seal caulk around the seam between the vent pipe and old rubber gasket. Then run a second bead of caulk just below the first bead.
    4. Slide the replacement rubber gasket over the pipe and press it down tight to the flange.
    • Difficulty: Easy
      The only difficult part is climbing onto the roof

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      Replacement rubber gasket, for installation over existing, leaking gasket

      Lap-seal caulk