I've had great success with warm water, and those spikey pipe cleaners. Be VERY careful using water, as you reallllllly don't want the wood to swell. Rubbing alcohol has worked for me, but not quite as well.
Remember, a good pipe has a layer of "Char" on the inside that protects the wood. Be careful you don't scrape that off.
Whatever you use (liquid), let it dry out for a good long time before using it. If the liquid/water gets into cracks and crevices in the cake or briar, it can crack the pipe when lit due to expansion (liquid into gas).
is this a wood pipe? If it's glass or metal I reccomend boiling it in water for a LONG time and scraping out the goop with stainless piano wire or old guitar string. if it takes any significant effort to scrape, boil longer.
If it's and old corn cob pipe, don't use any cleaners!!!! the cob will begin to fall apart.
If it's an old (and rare) alabaster pipe, again NO CLEANERS. In fact I wouldn't even try to scrape it much. Those things are extremely fragile. Go to the old school tobacco shop and have the owner help you clean it
Scrape it down to the char (the caked stuff in the bowl), but no further. If you have a lot of plugged stuff in the stummel, or the mouthpiece, high pressure air works well.
Try some rubbing alcohol, and then let it sit for a few days.
For cleaning old pipes that are no longer smoking sweet, fill the bowl with salt and then soak heavily with rubbing alcohol. Let it sit for several days and the bitter tars will be pulled out of the cake and left in the salt.
for any pipes, i prefer to avoid fuzzy pipe cleaners. they tend to shed. I have used the brass version before. I think they're intended for gun parts or maybe acetylene torches... something like that.