I've been using Dawn for washing hands, anything with grease or oil (motor or cooking), road grime, pretty much everything since about 1981.
It all started when I worked at the McDonalds in Morganotn, NC and they ran out of the McDonalds specialized floor soap. The manager told one of the guys to run across the parking lot and get a couple bottles of Dawn. The used the Dawn to mop the greasy build of grime behind the grills and it actually worked better than the stuff the McDonald's Coorporation forced them to use.
Ever since then, I was 100% sold on Dawn for removing any kind of oil or grease (cooking or motor). It's great for cleaning up fire place soot too. If Dawn will not clean it, the next step is gasoline to cut through. Things like varnish, oil based paints, and construction glues can only be removed with something like gasoline.
We keep a bottle of the Dawn foamy at each sink and bathtub and shower in the house and camper. I even keep a bottle at the outside sink in the camper. It goes without saying, we go through bottles and bottles of the Dawn foam refills!
AND, there was discussion on black tank cleaning about a month ago and Dawn was in the hot seat! Personally, I have found Dawn works marvelously in the black tank. Drain the black tank, flush it out, add about 4 or 5 gallons of water, about 1/3rd cup of Dawn down the toilet and go for a drive! Yea, it will bubble, but this amount will not over bubble, as one poor poster on these forums experienced, when they added too much and it bubbled back through the toilet and into the trailer. The right amount will clean out your black tank marvelously, keeps smells away, and not over bubble. Safe for the environment, and very reasonably priced!
I'm a believer in two products for my Camper and, really everywhere: Dawn and Mr. Clean Magic Eraser. Between these two products, you can clean almost everything.