I am an N scale modeler. I have both Athern and Deluxe inovation Conrail twin tub coal porters. I have just finished up my track work at the power plant. I was dragging a few around to test the track. It dawned on me these to not have the typical painted ends to indicate the rotary coupler.
How did conrail mark the ends with the rotary coupler.
Ooops! never mind. [D)] I thought those round “tubes” on the bottom were quick dump doors, but they are not, just extra space for coal to give more stability to the car.
They could uncouple the cars to turn them in the dumper, this was done with other types of cars like unloading woodchip cars in rotary dumpers that did not have rotary couplers. This would be a pain with the long 100-car unit trains, but doable especially at smaller installations.