The CMSNL image is nice. The block attaches to the frame, you can see the visible long side has a gap below the top. The tank rear has an open rectangular box section sticking down that fits into the rectangular groove on top of the block, and a metal tab sticking out toward the seat: you pull the rubber bar above that gap back and over the tab on installing the tank. It's a pain to pull it back over the tab again for removing the tank, particularly when the rubber is cold.
