</font><font color="blue" class="small">( He says my pressurized remote drainage field makes maitenance pumpout unnessessary in my case. )</font>
I don't see why that would be. The purpose of a septic tank is to separate the liquid from the solids by anaerobic biological action. The scum floats, the sludge sinks, and the exceedingly nasty liquid goes out to the drain field (or leach field as it's often called) If the scum blanket gets too thick, it can block the inlet line or go out the outlet line. If the sludge gets too deep, it can carry over and go out the outlet line.
If you get enough solids into your drain field, you build a new drain field. /forums/images/graemlins/frown.gif
All this is true, whether you have a conventional septic tank, or a pumped system. You must pump it out before the solids wreck your drain field. How long depends on your household practices and a certain amount of luck.
You can measure the scum and sludge levels by sticking a towel wrapped stick down the manholes. If you're not gonna pump, you should at least stick your tank every year or so. Eventually, you'll know how quickly the crud builds up.