I always find these discussions comical and they always follow the same path to thread closure.
Before the lock, let me say that I have dumped gray water many times and in many places. I doubt anyone would advise discharging an entire tank at one time and location. But if you park with an empty tank and then run an open drain into the bushes it isn't likely to be a problem. Use reasonable care and consideration for the next camper.
BTW, my Aliner doesn't have a gray tank nor do most pop ups or even many pre 1970s TTs.