If you turn on the correct two valves out of the eight valvs at the top, water will flow out of all of the exit pipes at the bottom.
If the pipe splits into two, the water will flow both ways, but only in a downward direction.
Touch a valve to select or deselect which pipe you will send the water down.
Figure out which two valves are the correct ones.
The quickest way to solve this puzzle is to trace the path of each pipe in turn to see which exit it leads to.
Let's look at the exit pipe two away from the left.
There are three pipes that lead here.
Follow the pipes up from the bottom to figure out which valves lead to them.
One of those three forms part of the answer.
Continuing on from hint two...
Let's look at the exit pipe two away from the right.
There are two pipes that lead here.
If you follow the pipes up from the bottom, one of the valves you reach is the same as one you figured out in hint two.
But that's not the one you're after.
The valve that forms part of the correct answer is the other one.
Continuing on from hint three...
The valve you figured out in hint three was G.
The pipes that are no connected to G come from the valves you figured out in hint 2: B or C.
Choosing on of those will give you the right answer.
Answer for 'Pipe Nightmare 2'
The answer is 'CG'.