Shut the outflow valve | Mission 3 - American Consumption Splinter Cell: Blacklist Guide

You now need to return o the area where you earlier started the exploration of the area to the right of the control room. Stop next to the corner again and hide behind the cover shown in the screenshot. Wait patiently for the guard on the lower level to start going right. Only then, jump over the balustrade and turn left.

Climbing over the water pipe

Go ahead and keep monitoring the remaining enemies to the left. Jump over the balustrade and take the stairs. Do not take the passage to the location on the left, this time, and take the alternative route to the target. This means that you should turn left and move as close to the right wall as possible. After several moments, you should reach a drain pipe hidden in the dark. Grab onto the pipe and climb up, thanks to which you will return to the control room.

Once again, go to the area to the left and approach the ladder that you used at the very beginning of your visit to this location. Just like earlier, you can't be in too much of a hurry, because there is a terrorist around. Wait until it is safe here and, only then, go for the door shown in the screenshot. Close the door for safety and interact with the valve, which will result in the completion of this mission.

Reception of the sonar pulse

After you return to the mobile command center, make sure that you perform all of the standard activities (conversations, purchases etc.). In accordance with the information that you received, it is a good idea to receive the Sonar Pulse from Charlie. This piece of equipment is useful in case of detecting the enemy units (if you have already bought such goggles, you can skip this step). After you have dealt with all of your business here, interact with the SMI and select the optional or the main mission (Private Estate).