In time, a faithful briar pipe will develop a sour, used-up flavor. This is caused by the oils in the tobacco, which can go rancid; by tar deposits; and by the various flavors of tobacco mixing. To sweeten a pipe is not to add any flavor, but to clean it of oils and deposits. Even the most expensive commercial sweeteners are alcohol-based, and veteran pipe smokers will use Scotch, Vodka and rubbing alcohol to do the job. Some will use an aggressive salt and alcohol treatment.
Allow the pipe to cool down completely since your last smoke.
Remove the stem from the pipe. With your choice of liquor or rubbing alcohol, wipe down the outside of the stem and the shank (the shaft that fits into the briar bowl), until your rags or paper towels come away clean.
Dip a pipe cleaner in your chosen alcohol, and clean out the stem and shank.
Repeat with fresh pipe cleaners, until they come away perfectly free of stain. Repeat a last time with a dry pipe cleaner, to remove any moisture.
Sweeten With Alcohol
Ream the pipe, leaving a 1 mm layer of dottle (the carbon buildup that protects the briar wood). Replace the stem, and push a fresh pipe cleaner into the stem. Find a way to sit the bowl upright. A good technique is to fill a soup bowl with uncooked rice, and rest the stem on the rim of the bowl.
Fill the bowl with your choice of liquor (Dewars Scotch whisky or bourbons are popular). Allow the bowl to sit from eight to 24 hours; refill with alcohol as needed. (Alcohol evaporates quickly.)
Dump out the liquid; it should be dark in color, and may smell nasty. It contains the oils and other deposits that imparted that sour flavor, but it has not dissolved away the dottle. Wipe out the bowl gently, without wiping away the dottle, and use a few pipe cleaners to dry out the stem. Allow the pipe to air dry completely, overnight. Your next smoke should taste much better than your last.
Sweetening With Alcohol and Salt
Ream and rest the pipe as in the steps above.
Fill the pipe bowl halfway with alcohol, and fill to the top with salt.
Allow the pipe to rest for between eight and 24 hours, or until the alcohol has evaporated and the salt has dried completely. You should be left with darkened, dirty-looking salt.
Wipe away, dump out, or otherwise remove the salt. Use a soft cloth soaked in alcohol to remove any remaining salt in the bowl. Use alcohol-soaked pipe cleaners to remove fresh deposits from the stem and shank. Allow the pipe to dry completely, overnight. If you taste any residual salt, this should go away in a few smokes, or you can clean out the bowl and stem once more with alcohol.