Drain Schematics

Details
As a prerequisite to this item dropping, you must have completed the quest Quest:As the Crow Flies, given by Ysiel Windsinger in the Cenarion Refuge in Zangarmarsh.

This quest given by this item ultimately leads to one of the quests available for the Coilfang Reservoir Instance Hub.

Source
This item drops from Bloodscale Nagas and the Steam Pump Overseer Nagas in Zangarmarsh.