Good freakin lord, folks- just think it thru...

Place rw cube on top of hydroton.
Hand water rw cube. Water will pass thru cube, cascade over hydroton.
Roots will grow out of bottom of cube.
Roots will grow thru hydroton.
Roots will emerge from bottom of net cup.
Roots will grow down into solution.

You will need to hand water the rw cube about once a day for about a week.

Not rocket science.

Don't overthink.

rw sitting on top of hydroton will not hold water for as long as rw sitting on a dinner plate. Rw on top of hydroton ( or otherwise able to drain properly) is actually kind of tough to overwater- excess runs out the bottom, if there's a place for it to go.