My son helped me to make it during a new year vacation.
Seven years have passed since that, and several problems have occurred,
including rotting of its wooden cover, leaking of water which made the ground soaked, growing weeds just beside it, etc.
In addition, the wooden retaining wall of blueberry plot has become to rot.
So, I decided to lay a concrete foundation under the bath tub, and to add reinforcing concrete blocks to the wooden wall.