PART 1: TURNING YOUR VALVE INTO A SWITCH
The first thing you need is a water valve. There are two common types of valves, gate valves and plunging valves. For this project, we need a gate valve (see video for details). Once you've got your valve, use a wrench (you might need a torch to heat it) to take it apart. Take off the flat/round piece and leave the t-pipe portion aside.
Then take your rotary switch and feed it though the 1"t-pipe with a 1"-3/4" hex. Using 1.5" of clear vinyl tubing (1/4" ID 3/8" OD), press the tubing over the tip of the rotary switch and then push the tip of the valve in the other end of the vinyl tubing to attach the two pieces.
Once you have your rotary switch attached to your valve, place some JB Weld on the threaded part of the valve/hex pipe to hold the valve in place. Also place some JB Weld on the bottom of the rotary switch so it stays firmly in place inside the t-pipe.