Get hold of some Gas Fitting Tape,[yellow] this is .004" thick cut a small length and roll it up into string form..3 turns around the glass will work fine for ever..
dont use the common el-cheapo water seal tape [white] its very thin and wont roll /string up..
Hmm, I use the common white teflon tape extensively, and have had no bad experiences. I even spin it into round strings for "piston rings". I do find the tip for yellow gas tape interesting though, and will look for it. But I would not hesitate to use the white, if I had it laying around, as you can understand.