Just find something long and strong enough to scrape the sides of the metal tube stem. It's impossible to get all of it, so when the rest is impossible to get off, get some Isopropanol Alcohol/Rubbing Alcohol, it comes in 70% and 99%, get the 99%, and it's sold at most drug stores. Soak your stem piece in that that. The take some hot water or boiling water, with some salt, and rinse it out really well.