How was water drained from the Great Bath in Mohenjodaro?

Flowed into a huge drain.

As for the Citadel, it contained structures that served special public purposes. Among them was the warehouse, a massive structure with preserved lower brick portions, while the upper portions, likely made of wood, have decayed over time. Another notable feature is the Great Bath, a large rectangular tank situated in a courtyard, surrounded by a corridor on all four sides. The tank was made watertight using bricks set on edge and a gypsum-based mortar. Steps on the north and south sides provided access to the tank, and rooms were present on three sides, one of which housed a large well. The water from the tank flowed into a sizable drain. Adjacent to the northern lane, there was a smaller building with eight bathrooms, four on each side of a corridor, each with its own drain connected to a central drain along the corridor. Due to its unique design and its location within the Citadel, scholars suggest that the Great Bath served a special purpose, possibly related to ritual bathing.