This is something I was wondering - do the roots already have to be long enough to touch the water before I place them in their pots, or will they somehow find their way through the dry hydroton? :S
The roots will definitely search for water. Like suggested above, top feed until the roots reach the bottom of the net pot.
When i did dwc, I'd leave an inch between the water and the bottom of the net pot. The airstones pushes water to the top and when the bubbles reach the top, they pop and water hits the bottom of the net pot.
I think that inch gap in dwc is crucial but some people have their own ways of doing everything. Whatever works really. Trial and error lol