What is the best and easiest way to get solder off of the thread of the fitting that soldered to my existing pipe? The fitting is in a vertical threads down position and some of the solder ran down onto the theads and the pipe plug will not thread into the fitting now.

Also, how should I have proceeded in the first place? Should I have soldered the fitting with the plug inserted in it. I did do that orignially because I thought the TEF tape would be destroyed and be rendered ineffective as far a sealing the plug.