http://www.rl180reef.com/pages/stand...n_stockman.htm
That's the page from Richard Durso's page. I would recomend cutting a box out of the pipe instead of drilling the holes. Keeps it from getting clogged, and I had fewer noise issues when I actually cut a big hole out, had a lot more trouble tuning it to be silent with the little holes drilled in the pipe.
Mike