The main push is from twin 25 hp pumps that feed into four large horizontal sandfilters which are backwashed twice a week. We also use ozone (much smaller pump) fed into a contact chamber, run into a destruct tower and fed back into the main return line to the tank.
Water is pulled from both an over flow skimmer as well as two main suction vents on the bottom. Water is returned to the tank via a reverse under gravel feed as well as a surface spray bar at roughly 1,100 gallons per minute or so.
If you are watcing the webcam today (and everyday from now on) at 2:30 PM (Central time in the US), you'll see me in the water feeding.