I have been on sites (main and CL/CS) in UK and abroad where they have asked for grey water to be used for hedgerows or young trees. Sometimes i suspect it is to keep their costs down as grey water put into the chemical waste would fill up the septic tanks, or affect the process.
Our grey consists only of water, washing up solution,soap, toothpaste residue, shaving soap etc. There will also be some small amount of food residue from washing up.No bleaches or strong cleaning agents are used when touring. We are a bit 'Grungy" I guess.
But if there is a grey waste point then we use it.