About halfway through Dead Island 2, there’s a quest called Flushed that sends you into the Brentwood Sewer. You’ll eventually come upon a sluice gate that needs to be opened, but first you must unblock the Main Septic Tank via the Hydrostatic Management System.
To access the Hydrostatic Management System, you’ll need a keycode. You can find it across the water from the Hydrostatic Management System, though you’ll need to reach through the iron bars in the window to reach the Instruction Manual. Here’s a video of the exact location of this manual:
Once you have the clipboard, you can use the keypad to open the door to the Hydrostatic Management System. The code is 161280, but it really doesn’t matter — your character will automatically type in the correct code once you’ve collected the Instruction Manual.
In order to unblock the system, you need to apply the right amount of water pressure to each pump. There are three pumps and three valves, and each one is labeled with a number.
Basically, the number on the pump is the amount of pressure needed to flush that pump, while the number on the valve is the amount of water pressure provided by that particular valve. In order to flush the pumps, you just need to apply the correct amount of water pressure to each one.
Here’s a video of the whole process, but I’ll walk you through it via text below.
Before you go unblocking the pumps, you’ll want to clean the caustic ooze out of the next room (note that you can access this room by smashing through the boards blocking the window — or you can just use the door). In the same room as the three pumps, there should be a valve that cuts off the flow of the caustic ooze. Once you turn that, ooze should stop pouring from the ceiling, but you’ll still need to clean the floor. You can do this by picking up one of the water cans and pouring the water onto the floor.
Once this room is clean, you can pick up the valve wheel, which you’ll need in order to turn the first valve. This first valve is marked with a 10, and so is the first tank. So this means you just need to turn the 10 valve in order to flush the first tank. The second one is marked with a 75, though, which means you’ll have to turn all three valves. 10+20+45=75. You already turned the 10 valve, so you don’t need to do that again, but the other two valves are on a timer, meaning you’ll have to turn them in quick succession.
The last tank is labeled 45, which means you need to turn off the 10 valve and then turn on the 45 valve.
And that should solve the puzzle and cause the sluice gate to open, completing the Flushed quest in Dead Island 2.
