If not cleaned regularly, tobacco pipes can develop a sour taste. After you have smoked your pipe and knocked out all of the ash, use a pipe cleaner and run it gently through the stem, pushing it back-and-forth several times. Use as many pipe cleaners as you need until the last one comes out almost completely clean.
Then take a pipe cleaner, bend it in half and swab the inside of the bowl with it, making one complete revolution in order to avoid building up too much cake, the carbonized tobacco that's stuck to the inside of the bowl.
Cake insulates the bowl and allows good air flow around the tobacco, promoting a clean, even burn. Cake also prevents bowl burn outs and keeps your pipe burning cool and dry.
Cake should be kept to a maximum of 1/16 of an inch thick, about the thickness of a dime. If the cake is thicker than that, it could expand while you are smoking the pipe and crack the bowl.
When the cake gets thicker than 1/16 of an inch, use a pipe reaming tool to scrape the cake back down to the desired thickness.
When knocking the tobacco ash from the bowl, be sure you handle the pipe by its bowl, and knock it gently against a surface. The best way to knock tobacco out of a pipe is to purchase a cork knocker from your local tobacco shop and place it inside your ashtray.
Don't leave unsmoked tobacco inside your pipe. It tastes bad and can hold moisture in your pipe, which you do not want.
After smoking a pipe, wait a couple of hours to allow it to cool before separating the mouthpiece from the bowl. You may break your pipe if you remove the mouthpiece immediately after smoking.
Once in a while, it's necessary to run pipe cleaners through the stem and shank of your pipe with some type of cleaning solvent in order to keep your pipe fresh and prevent it from absorbing the moisture that's generated by smoking.
There are several good cleaning solvents available at tobacco shops but you can also use alcohol that's more than 90 proof.
Whatever you use, it should be able to break down tar and resins, sterilize your pipe, dry quickly, be high in alcohol content, non-toxic, have minimal taste and not affect the finish on your pipe.