I found these pipe tips on the Bucharest Pipe Club's blog. I found them interesting and figured why not re-purpose them. Warning, much of the site is NOT in English so be forewarned if that type of thing bothers you...

Keeping Your Pipe Stems Shining Like New
First, we have to give credit where credit is due. This tip comes from the video "Total Pipe Care and Maintenance". We've all had our vulcanite rubber stems turn that nasty brown/green that happens over time. This is oxidization. Oxidization comes from the chemical reaction from the saliva in our mouths reacting with the vulcanite and from sunlight. This unsightly process can be slowed with a simple product that you most likely already have in your kitchen ... olive oil. This process is best done with a brand new stem or a stem that has been thoroughly cleaned. First, take the stem from the bowl. With your finger take a very small amount of olive oil and coat the outside surface of the stem. Allow the olive oil to penetrate for about 5 - 10 minutes. Now take a clean cotton rag and wipe off the excess. It's that simple! Here's why it works ......... If you look at a vulcanite stem under magnification you'd see that there are thousands, if not millions, of tiny pits in the surface, similar to an english muffin. This is normal. By applying the olive oil to the stem the microscopic pits get filled by the oil leaving less surface area on the stem for the oxidation to get a foot hold. You'll also want to keep your pipe out of sunlight, direct or otherwise, for any extended period of time.

The above tip is a great idea. However, I found the results of the following experiment quite interesting:

Leave It In or Pull It Out ?
Your pipe cleaner that is. One year ago someone emailed and asked whether or not it was a good idea to leave a pipe cleaner in the stem when you're through smoking. I answered according to what I had been taught ... NO. I've always listened to the pros and cons on the subject and formulated my own conclusion. After thinking about I came a the conclusion that I shouldn't be jumping to that conclusion. I decided to perform a somewhat controlled test. Here is how I did it.
-Two identical, new Savinelli Model 114 pipes were used. Both croos grained.
-Each was smoked three times a week for 1 year (3/03)
-Each rested 2 days between smoking.
-Each was cleaned with 4 pipe cleaners after smoking was complete.
-Each was thoroughly cleaned every 4 weeks.
-The same tobacco, Five Star Deluxe, was smoked exclusively.
-One was left to rest with a pipe cleaner in the stem and shank and one was not.
-Standard size and fluff pipe cleaners were used.
Here are my observations at the conclusion of the test. The pipe in which the cleaner was left in will be referred to as Pipe A. Pipe B is the pipe without.
-The shank of Pipe A is slightly darker than Pipe B leaving a slightly two toned appearance.
-Pipe A developed a slight gap between the shank and stem.
-Pipe A's shank expanded slightly larger than the stem.
-Pipe A had more pipe cleaner residue (stray fuzz) in it when thoroughly cleaned.
-Pipe B took longer to break in. I'm not sure if that had anything to do with the test.
-Pipe A took a few more cleaners for the once a month cleaning.
-After 1 year Pipe A is a little more ... well for lack of a better term, stinky.
So there you have it.
Pipe B, without the cleaner, faired better than Pipe A with. I am only going to guess why but I suspect that the pipe cleaner left in does more to keep the moisture trapped than it does to wick it out...Happy Smoking