Grey water disposal locally used to be legal to discharge into a wooden "soapbox". However, when things were "deregulated" the responsibility for install, repair, maintenance etc was given to "authorized professionals" who charge an arm and a leg ($15k and up), and you can no longer install or even fix your own system, unless approved by an AP, and there's no incentive for them to let you do that (you used to be able to install your own with design input and an inspection from the local health inspector.
My property has five septic systems previously installed in the 70's - I am using one for the house, one for the cottage, one for the shop bathroom, one for the RV pad/sanidump, and I have one that will serve for a "clubhouse" type recreation building in the future. My property is also nothing but gravel, so drainage is excellent and the systems should all run forever - if one does fail, I'll plumb it 100-300 feet into the next closest system. Each is pumped out every 10 years and gets a dead chicken or coon or possum occasionally for bacteria.
For my hunting rig greywater I dug a hole in the sand next the parking spot, buried a plastic 50 gallon drum perforated with 1/2" holes for the top 1/4, with an inlet at the top, and surrounded by a couple yards of 3" rocks and landscape fabric. Works like a dandy.