The urea itself is in such a low concentration that you could probably drink it. It's the minute stuff in there that will probably kill you though. If you get in an accident, there may be some slight spillage but clean up shouldn't bee too bad. Although as protected as those tanks seem to be, if it ruptured in an accident, I don't think you'll have to worry about clean up.
Edit: Just looked it up and the solution is 32.5% urea and 67.5% deionized water. The MSDS lists a health rating of 1, which menas that it is as hazardous as water. If you don't sleep with your face in it, it probably won't hurt you.