Air Control Valve
I've tried using an air valve instead of just a drilled hole (pictured left). This allows for quick and easy flow control settings and fine tuning of the water level in the chamber. It also has the advantage of not having to figure out the proper hole size to use for the air hole in the end-cap. However, it has added maintenance in that it requires a cleaning from time to time.
To add a valve just drill a hole in the end-cap that the air valve will fit snug into. Use a little crazy glue to hold the air valve in place. Makes sure the seal is air-tight. On top of the air valve use standard airline tube. This protects the valve opening which helps to reduce salt creep from plugging the valve.
A different twist is to insert the airline tube directly into a hole drilled into the end-cap. Then attach the air value to the end of the tubing. This helps to keep salt creep off the value.
When you notice the water level in the overflow chamber getting lower, its time to clean the valve.