If you find yourself chasing down Minsc after running into him at The Counting House in the Lower City, you will find yourself looking for him in the Lower City Sewers.
As you follow his trail, you encounter a section of the sewers where a Sluice Gate may be found but to pass, you need to open it before you can reach the Cistern.
This acts as a sort of puzzle that you need to complete, which simply requires you balance out the pressure to safely open the Sluice Gate.
How To Open The Sluice Gate?
The Sluice Gate will only open once the Water Level and Temperature Level are perfect, which means both the Water Level Valve and Temperature Valve need to be interacted with.
Interacting with a valve will cause an increase and interacting with it again will stop it from increasing, which will allow you to control what level they are at.
You will need to make sure that the levels do not go over and that both meet a perfect balance so that the Sluice Gate opens.
This simply requires you to open a valve to increase the water/temperature level and shut them off to allow them to go down until both are matched.
How To Balance Water and Temperature Levels?
Interact with the Water Level Valve first as it takes longer for the water level to increase and quickly interact with the Temperature Valve afterward.
Once the water level has reached the correct level (represented by the dial going into the center of its gauge), turn off the Water Level Valve.
Wait for the Temperature Valve to do the same and once both have met the correct levels, they will gain the conditions called Perfect Water Level and Perfect Warmth.
Timing is important in this part, and it is necessary to turn off a valve before it goes beyond the safe point or else you may have to start again.
Making a Mistake with The Valves
If you go too far with either the Water Level or the Temperature Level, this will cause the valves to break temporarily.
The Water Level Valve will become flooded, which can knock you down to the pit below or the Temperature Valve will overload, causing a small explosion.
Should this happen, you won’t be able to adjust the valves and will need to interact with the Emergency Release Valve on the very right to reset them.
Verdict
Opening the Sluice Gate is easy if you understand how the valves function and it is best to keep in mind that these may be turned on and off. (They continue to rise when left on)
Since the Water Level Valve is slower than the Temperature Valve, it is best to increase the water level first and turn it off before adjusting the temperature.
Making your way through the Sluice Gate is one of the two possible ways to gain access to the Abandoned Cistern.