With a couple of special projects in mind I needed to dismantle a spectrum tank car. Considerably more involved than the average Big-hauler. Like most Bachmann products there is very little glue. Construction is done with screws or press fit. Not all of the screws are visible in the beginning. The truck screws do not go through to the tank. They are only attached to the frame. With the trucks removed I could see that the frame was held on by a screw at each end and the tank held together with two other screws located beneath the frame webbing. You can see about half of those holes in the second figure.
In addition to the screws the tank is held to the frame by the brake chain, tank bands and screws at the base of the ladders. I removed the chain from underneath since it required me to bend the last link open. The bands are attached using a small plastic pin. I will have to glue these when I am ready to reassemble. They are probably a press fit but I could not get mine to pull out. Others may have better luck so I recommend trying.
Tiny screws hold the ladders and walkways on. You can see them at the blue arrows in the first picture. The top of the ladders are held on with plastic tabs under the walkways. These are passed through holes in top of the ladders and then melted. The handrails are two pieces passed through loops in the ladder frame and then held on by the stanchions. The stanchions are press fit and can be pried out gently. The last piece is pressed in as shown in the bottom picture. Removing all of these will allow the frame to be separated from the tank.
To get the tank apart remove the two large screws in the deep recessed holes. The walkway is secured inside of the tank by three screws along the center line. With these removed it will lift out with the coupler chains still attached.
The rest of the small details can be gently pried off. Sometimes a small amount of glue is used but this rare and not normally a problem.