This topic is worth putting some popcorn in the microwave and popping a cold one. Many valid posts here. Got to put in my two cents worth.
So, how do you define grey water? Here is the setup. I'm staying in a county/state campground. Many have water and electric on site and dump on the way out the gate. I go hiking or ATVing and I return to my site at the end of the day. I've got water left over from the RV. Technically, that is grey water. How do I dispose of it?
Here's another one. I turn on the hot water and let it run into a pan while waiting to shower, cook food, wash dishes, wash my face, etc. Technically, that water is grey water since it came out of the faucet.
I challenge you to actually collect and measure how much "grey" water you collect in a given day using the two above examples. Mine runs almost 4 gallons a day for two people. Seven days and I've almost filled my 30 gallon tank with non-grey water.
The last thing I would do is dump the "big one" anywhere except where it is supposed to go. Besides, 30 gallons of black water is a lot of "stuff".
I know what you and I both do. There are laws and then there is common sense.