truth: dirt and other solids settle to the bottom. the effluent floats to the top, then the tank makes the initial breakdown using anaerobic bacteria (water breathing.) the stuff then flows under the barrier and up into the drain pipe. the drain field then completes the breakdown using aerobic bacteria (air breathing.)
you'd almost have to see richard's diagram to completely understand this process. it looked something like this:
for those who are interested in reading further about septic systems, there is a really good site:
http://www.apalacheeseptic.com/septic-info.htm
