Firstly, this:
I see everyone saying to boil it. You dont have to in fact sometimes boiling a pipe, is too much thermal shock for the glass to quickly, and the pipe will break.
Second, I am suprised no one has mentioned white vinegar water? This is all I've ever used, it breaks down that resin like a charm and it just falls right off with the touch of a q-tip. Just let it soak for a few hours in a jar. That, and vinegar is less harsh and safer. I use it to clean all sorts of stuff.