Rob,
<font color="blue"> Do they have to unhook the cars to turn them over? </font>
No, that was the fascinating part. All of the cars are painted or identified on one end with a Yellow stripe/paint/decal, whatever. If they are all connected properly, the yellow end is facing the dumping operator. In this orientation, they can be turned upside down, these went approx. 150-160° upside down. If one of the cars are connected backwards, it could flip the car in front or behind it. The couplers have a rotating sleeve to go one direction more than the other.
The dumper can be all automatic or operator controlled. My Buddy prefers to do it manually, otherwise it's too boring to just sit and watch the computer do it all.