This site has been invaluable to me so I thought I should pass on a simple mod that has worked perfectly for me. The pictures are pretty self explanatory, but it works by venturi and is fully adjustable from full open to completely closed, and all points in between. Not only does it serve a great role in ph control with fine little bubbles, but it is pretty cool looking and fun to swim in. Enjoy! Also I felt confident drilling into the "eye", since the entire return fitting is $4 online.