This time My son hit a curb block and knocked the plastic skirting from under the drivers side. They were driving and dragging parts down the highway. When they came home my son shows me a black plastic tank about 12x12 that fits under the air cleaner box underneath the battery i think . I do not know what it is. It has a filler neck that sits up in the frame and some holes on the bottom. never noticed it before. The mounts for it are snapped off. any clues what it is?