Get some of the enzyme stuff that breaks up the poop and use it.
Find rubber/neoprene/similar gloves with the longest gauntlets up the arms that you can. Keep them, a roll of paper towels, and some waterless hand cleaner in the area - I found room in the "electrical closet" behind the water supply/tank dump closet.
Stand where you won't get wet.
When you hear the last of the liquid from each tank, give it a few more minutes, because it's still draining.
If possible, drain the tanks before you start for home. Nothing makes you quite so popular at roadside restaurants as the aroma of a black tank venting out the top of your rig.