Thanks for the help latewood. I have some pumps I use for AC installs that collect condensation from AC equipment that i'd like to try using. In this diagram you'll see what i'm looking to do. The view of the diagram would be from the side of the garden.

The nute solution would start in the holding tank above the garden on a shelf, gravity down to the plants through the same 1/4" tubing/elbow like you said. Then it would drain out of the bottom of each plants container (5gal buckets) into the pump below. The pump has a reservoir built in as well as a float switch, so whenever the nutes drain all the way to the pump, once the reservoir is filled (1 gallon) it will pump it back up to the holding tank. The pump is made of PVC and made to run ALOT, and I would expect it to be running at least every 10-20 minutes, but like I said, thats what they do under thier normal load in thier normal settings.
http://img225.imageshack.us/my.php?image=gravity6oh.png
Heres a diagram of what i'm looking to do. My only real question is, that I plan to put an airstone/bubbler with an air pump in the top reservoir, but wouldnt that just hold all the oxygen at the top of the system since air wants to float to the top? Or would the mixture of oxygen be fine enough to flow down together? What do ya think?