If you look closely at this photo in full size, you can see the tracks/rails on the back of the coaling tower. Because we were limited on space, and the tracks are on a curve, we modeled this facility so the coal cars unload/dump to a pit directly underneath the coal tower. The bucket (which really doesn't exist on this model) is down in the pit to raise the coal to the top and dump inside the tub. There is no chute underneath the center anyway, so we unload raw material underneath, and load the engines with the chute on the outside (outbound) track.
Just like the sand house not being next to the track, we will use a conveyor to unload the sand hopper to transfer sand to the sand bin. Not really how we wanted to do it, would rather have the sand bin right next to the track, but because these tracks are on a curve, the articulated engines would not clear the structure.
In the real world, a lot of these service structures were crammed in small spaces, even more so in the O scale modeling world. We had to get them all in, with limited space, so the imagination has to come into play a little bit here.