I have no problem recycling RV gray water onto grass, shrubs and trees. Plants will thrive on RV gray water if you don't use harsh soaps or chemicals. Your gray tank holds shower water, laundry water (if you have a washer and dryer), dish water, teeth brushing and hand washing water. If you think about it, that amounts to a lot of water usage. Selecting plant friendly biodegradable detergents and soaps will allow you to recycle this water instead of allowing it to go to waste.
I've stayed at many campgrounds that didn't have sewer drains at the campsites. We can usually go two weeks before having to dump our black water, but the gray water tank will only last about three days before we need to empty. I'm too lazy to pack everything up and go to the dump station, so I water the surrounding vegetation with our gray water.
You will need an adapter (sold at most RV stores) that will attach to a standard garden hose and to your black/gray water drain pipe.If you didn't already know, there is a controversy surrounding this idea. Some parks forbid the practice and some people argue that it is unsanitary. I don't let the hose sit in one place causing a puddle, but move it around to different plants until the tank is empty. In many parts of the country water is in limited supply and recycling gray water makes more sense than sending it down the sewer to a treatment facility.
When I'm at a fairground or outdoor event that has RV parking on the grass, I use a short hose to drain my gray water tank directly under the RV. By doing it this way you don't encroach on your neighbor's space. Instead of throwing an old hose away, I recycle it for this use.I know some folks object to this method of disposing of gray water and that's why it remains a controversy. Because of waterborne diseases like cholera, you should always dispose of black water into a sewer system. Gray water on the other hand has far fewer contaminates and in my opinion is safe enough for recycling. As long as you are not offloading gray water near water sources such as a lake, stream or a well, there should be no problem.
Covering the gray areas of RVing - Jim Twamley, Professor of RVing