I would recomend getting a clear elbow or 22 degree connector between the hose and your waste connection on your trailer. I find it very helpful when rinsing out my black water.
However, I keep both valves closed until I need to dump, and then I dump the gray first for just a few second to make sure everything is setup properly. It's always better to know if something is wrong with a pipe connection with gray water in the pipe than black water in there. I also keep some disposable gloves in the trailer for when i'm dumping. They are cheap at an auto parts store ( VIP, auto Zone, ect). However, I just go on weekend trips and I never fill the tanks over a normal weekend.
I do have a question for the masses: Does bleach hurt the tanks? I like to put a cup of bleach in each tank mixed with a gallon of water between trips, and before i leave i just drop a little blue bag of tank treatment in there (it use to be the blue bottle of treatment, but the bags are just easier).