I'm in the process of moving my septic and the soils engineer told me that in my rural county, it was illegal (without a special permit), but practical to run grey water to a French drain-basically a deep pit filled with gravel. He said by diverting the phosphate laden grey water from the septic tank, the septic system would last much longer. I also know someone who grows endangered pitcher plants in north Georgia in his own back yard bog on only grey water. These bog plants love wet conditions all year round.
Are you rural or in the city? What kind of climate?