Soft cotton pipe cleaners
56 per pack
After you remove the stem from the pipe, run one pipe cleaner through the mouthpiece of the stem and pull out the other end. Take a 2nd pipe cleaner and insert into the shank of the bowl and twist, absorbing the tars and moisture in the tunnel of the pipe. Remove that pipe cleaner and with the 2nd and clean half of the cleaner, wipe the interior sides of the bowl but do not scrape so that you can build the "cake" over time.