i have usually thought this verse explains tao as being before existence, "it is the forefather of the gods". i would liken this verse to asking "what was before the big bang". Tao is clearly more than a term used to make the indescribable describable, this verse clearly states it is a limitless pool from which all existence derives from. i would almost be tempted to call tao vacuum energy (http://en.wikipedia.org/wiki/Vacuum_energy) from the description in this verse.
@Einar with thanks to Ron
"How much Tao is there? More than you'll ever need. Use all you want, there's plenty more where that came from.
You can't see Tao, but it's there. Damned if I know where it came from. It's just always been around." http://www.beatrice.com/TAO.pdf