The side walls of the tank were constructed with finely fitted bricks and a thick layer of bitumen (natural tar) was laid along the sides of the tank to keep water from seeping through the walls and up into the superstructure.
The SD Area of Mohenjo-daro.
The tank would have been open to the sky, but the surrounding structures would have been roofed. The sidewalls and parts of the floor have been conserved using modern replica bricks.
At the southwestern corner of the sloping floor, a small drain first passes through the massive walls of the tank and connects to a corbelled arch drain that curves along the edge of the northern terrace of the granary to the west.
The floor slopes down to the southwest corner where a small outlet (top right) leads to a brick drain, which takes the water to the edge of the mound.
Built on top of a tapered brick platform, this building had a solid brick foundation that extended for 50 meters east west and 27 meters north south.