When our gray tank gets full (it takes five days) and we don't want to go to the dump station quite yet, we use a bucket to dump gray water into the toilet, since we always have a lot of extra black tank capacity. Plus it helps rinse out the black tank with soapy water, which is not a bad thing.
Gray water can attract bears -- they are known to break into cars when they smell cosmetics and toiletries, so the fragrance of soapy water would have the same effect, I would think. And if you add in food particles, it would be even more dangerous.
For the same reason, if at all possible, take the trash out of your RV at night, if you have had a fragrant dinner. We had smoked barbecue ribs one night in Sequoia last November, and left the bones in our trashcan inside the trailer -- we decided not to take out the trash because there was a howling snowstorm. Not a good decision. A young bear (a yearling) smelled it and tried to break in while we were sleeping. We scared him off, but lesson learned.