All underground piping in connection with underground tanks shall comply with the following:
1. Piping shall lead out of the top.
2. Piping shall be covered with at least 1 foot of earth or 4 inches of earth and 4 inches of concrete except for necessary riser pipes.
3. Piping shall be equipped with means for disconnection.
4. At any point of change from the vertical to the horizontal or from the horizontal to the vertical, there shall be installed an approved flex connector assembly.