The World of Waterfalls has been to this waterfall, which you can read about here.

I constantly see people hiking/walking into Maunawili from the main highway(Pali Highway). This is a really long walk before you even get close to the beginning of the trail. You should really Google map this before starting your adventure. There is a city bus that will get you most of the way in but it comes by very infrequently. You can get the schedule here: http://www.thebus.org/route/routes.asp