Zhuangzi concludes his story of Liezi's conversion with what amounts to a summation of his mystical vision. I call it mystical because it is much more than a "philosophy of life", an intellectual paradigm, although it is this that points him in the right direction, provides his gate. It is mystical in that it is an experience of existential liberation facilitated by going beyond the limits of the egoic-self into which we as a species have evolved. If mysticism requires union with 'something' outside ourselves, however, then it is not in this sense mystical. The only Dao that Zhuangzi suggests we realize is psychological Dao, a transformative way of being in the world facilitated, not by union with a metaphysical Dao, but by the very lack of a need for such a union. Not-knowing and Drift and Doubt are his gates to this experience and they remain on the other side. I admittedly harp on this interpretation because it is the only one that makes his way accessible to me — and because I honestly think this is what he teaches.
None of this means that a metaphysical Dao is not in some sense assumed; it is. Dao is Reality; Dao is thus what we are and what we do, whatever we are and do. We cannot stray from metaphysical Dao; we are Dao, just as all things are Dao. There is no disconnect; there are not two. There is no hierarchy of being; nothing is more real than anything else. We cannot unite with what we already are, at least not 'essentially' as with some "true self", but only existentially with the self that we are. How do we know this? We do not. It can only be experienced, not known — just like life itself.
Thus Zhuangzi concludes: "In this way, wholeheartedly embody the endlessness and roam where there is no sign, fully realize what is received from Heaven, but without thinking anything has been gained thereby. It is just being empty, nothing more." (7:13; Ziporyn)
You can check out Scott's writings on Zhuangzi here.