[quote user=“dknelson”]
Athearn made, and perhaps still makes, a grain boxcar that I think has plug doors but also a small upper door at the top of the regular door (whether this is on both sides of the car I do not recall) that enabled the contents to be tested before unloading. A grain facility would be reluctant to potentially contaminate existing stocks of grain by just unloading any boxcar that said it contained grain, so the load would be tested, whether or not the car had that special small door.
My recollection is that a flexible tube would load the grain in an opening left in the temporary grain door, then once the car was full that opening would also be sealed and the doors closed. Assuming the load was accepted my recollection is that they would smash out the temporary door and the grain would just pour out (the car would be standing over an open pit, at the bottom of which was presumably some sort of conveyor system or screw). Then crews with brooms would enter to finish up the job. So at an unloading facility you would have boxcars, remnants of grain doors, some spilled grain, and guys with brooms at the ready.
Jaeger makes Signode grain doors in HO by the way.