Step 1: Turn on power by activating both switches on the seperate sides of the sewer system.

Step 2: Pickup the Keycard located on a table inside the apartment (above the buildable bench)

Step 3: Go the 'Mud Separation Room' located in the left hand sewer system (the side with Deadshot Daiquiri). Swipe the keycard to open the 'Mud Seperation Room'.

Step 4: Interact with the lake pump generator. This will initiate a short lockdown.

Step 5: Returning to the surface, go to the lake where a portion of the water has been drained revealing a concrete structure. Throw a grenade at the structure to blow open the hatch. You will know this step has completed as the screen will shake and smoke will continuously billow from the structure.

Step 6: Go down into the sewer system into the Juggernog Room and the ventilation door will now be open