Here in Texas, due to abuse and polluted waterways, the state actually does have some regulations in place for septic systems.
My personal recommendations:
1: If you think you need a 500 gallon septic tank, install a 1000 gallon.
2: Have at two leach fields, and a valve to separate them. Every year, change the valve to go to the other field.
3: Pump the septic tank yearly, ideally before spring rains. It may not need to be pumped for far longer than that, but this is a measure of prevention, as the $250 for the stool bus visit is far cheaper than cleaning up a backflow in the house.