Bill, I have read extensively into grey water systems for conservation and other reasons. A dry well in some situations is a very smart idea. A scary application of grey water is irrigation, especially surface irrigation like spraying. Pardon me but this gets indelicate: E. Coli from washwater as well as viral contamination and some bacteria are not good things to spray on the yard. Especially if kids or pets could become contaminated. Just having someone in the household with a viral infection, flu or whatever, is a source of dangerous contamination. Subsurface irrigation is far less dangerous but is still questionable for vegies you will eat. There are stringent filtration requirements with using grey water for spraying, soaker hoses, drip, whatever. I have seen several folks try and fail at using grey water for irrigation due to lack of sufficient filtration. Thosands of dollars and lots of frustration, wasted.
I intend to plumb my house while being built to accomodate a grey water system even though some septic engineers (civil eng specializing in waste disposal) have recommended that you not cut down the quantity of water feeding the septic system too much. I may opt for a not too hard to clean reusable filter and sand bed combination. I would still like to use grey water for trees and ornamentals even if I now think I should avoid it in the garden.
I'm not as fanatical as some on the conservation scale. People plumb homes to flush the toilets with grey water. One design had dual sources for flushing. Vaves selected fresh or grey to fill the toilet tank. The idea was to use fresh for the last flush of the day or as required to avoid putrefaction. Some folks install a holding tank for grey water and handle it in batches. One civil engineer writing aout health issues commented that there is no such thing as a holding tank for grey water as the act of storing it for any reasonable length of time even less than a day would allow it to transform into "black water" and that in general, storage for more than a few hours was a bad and potentially smelly prospect. So what next, timers to flush the toilets with fresh water if the noxious odor sensor triggers it? By the time the grey water gets filtered by the biomass of my pecan trees I think the pecan pies will not be harmed.
Patrick