I have been using McCormick's Rum Extract....which can be found in any large food market, in the Baking Section....for years to clean stems and smoke holes.
Also, you can use any grain alcohol products that you have on hand, high-proof vodkas, rums, brandy, etc. Many liquor/wine stores sell very small, personal nip-size bottles, of many popular liquors and liqueurs/cordials, etc. for a few bucks....so no need to buy a large, expensive bottle on booze that you might not drink.
I love to dip a pipe cleaner into some "Deep Eddy-Peach Flavored Vodka" and run it through pipe stems. Yum. I buy the small-size nips, and it lasts a long time.
Pipe smokers have many for "Everclear". Just stick to the GRAIN ALCOHOL (drinkable) products.