Had the same sort of problem with having a knot in one of my lines a while back. I did the spit and gentle chewing technique and it worked quite easily.
Here's the link to the thread with all the suggestions when I asked the same question...
In addition to tapping the knot a pointed but not sharp pick of some sort can help to loosen. Wifey has a manicure nail cleaner pick thingy which worked really well
Bit of dishwashing liquid and then GENTLY tap the knot from different angles on a smooth surface with a blunt object (back end of knife handle, or rounded bottom of a glass jar) trying to undo every few taps.
