First find out if its legal. Second, if it is and I dump it, will others be affected by the smell. If you pass the first two then I may dump, however I always make sure I have enough gray water left over to flush my black water which I dump at a proper location. Grey water does smell, but after it soaks in and drys on the surface I have never had a issue with odor.
If we fill our gray water and at a spot that does not allow us to dump it I have a shut off valve attached to the main outlet of the discharge pipe. I simply have it closed, open the grey, then the black and let gravity push some of the grey water into the black water tank. This has helped me get by a few days until I find a dump station.