The following chapter of the Control guide contains a walkthrough for a side mission called What a mess: Clear the Clog. You will learn, e.g. how to find the Clog and how to get rid of it.
To start the quest, visit Janitor's Office in Sector: Maintenance. The task can be picked up from the board.
Walkthrough: Go To the Maintenance Sector and proceed to the Pumping Station. Inside, you'll find a Clog that needs to be removed. Climb the scaffolding, remove the battery and put it in a hole in the wall. A new door will open - inside, you'll find another box.
Pick up the new box and throw it into the next hole. Now pull the first battery out and place it into the final hole.
Use the handle to unlock the door nearby. Go through the door and destroy the Clog below. As a reward, you'll receive some materials, a weapon mod and 3 skill points. Moreover, you can now visit the Janitor Office to get more "What a mess..." quests - you can find the walkthroughs in the dedicated chapters of our guide.