In the early 2000's Ronny Reich and Eli Shukron discovered and excavated a street and drainage system to the (north) west of the Pool of Siloam. This street led from the Temple Mount to the Pool of Siloam. Reich had excavated the upper portion of this street near the (south) western wall of the Temple Mount in the 1990's.
The drainage system under this street was evidently where some of the Jewish defenders of Jerusalem, in AD 70, hid from the Romans.
For a recent description of this street and drainage system see Hershel Shanks' article “Escape Clause,” Biblical Archaeological Review 36, no. 3 (May/June 2010): 45–47.