Setting up a Flood and Drain

I want to put 4 plants in rockwool cubes under a 4x4 scrog. If I just put a water pump in a smartbin and an air pump for oxygen, ran line to the tray and drilled a hole in the bottom for water to drain would I run into problems? Not to good with PVC and the fittings look foreign to me. I just want better efficiency in filling my screen, and giving up hand watering.

You need the tray to fill, and drain. If you don't have riser on you drain then the tray won't fill. Your drain line is only an overflow to maintain the correct flood level.
Once it's done flooding you need your water inlet line to be coming in from the bottom as well so that gravity will drain the rest of the solution below the riser on your drain
back down through your pump and into your reservoir.

Basically you need both your fittings to come in from the bottom. Your inlet fitting needs to be flush, and your drain needs a riser to set your flood level.
They sell kit's everywhere.

Just drill two holes in you bin, screw em in, hook the hose from your inlet fitting to your pump, and the hose from your drain back to your res.

Here's where I get mine.
http://www.ebay.com/itm/BOTANICARE-BULKHEAD-TRAY-KIT-1-2-3-4-FITTING-EBB-FLOW-DRAIN-EXTENSION-SCREEN-/170962371494?pt=LH_DefaultDomain_0&hash=item27ce26c3a6
10 bucks with free shipping.

The bigger fitting is always your drain fitting.

Were you baked when you thought of this because as the water goes into the tray it will immediately drain out. ??

stop killin the poor man lol