Dumping grey water in large quantities (500 gallons).

why would you ever need to dump 500 gallons at once? if you're dry camping in the sticks, just leave the gray valve cracked a bit, and a garden hose out to the bushes. a slow trickle from dishes or a shower is far better than saving it up and dumping it at once. I wouldn't worry about filtering the chlorine, hair or red blood cells.