Siphon tank, about 12 gallon dump each time. Too noisy for a display tank in a living space, I can hear it siphon from two floors up during the night when the house is quiet.
Leslie, I saw Pierces surge. I had also set one up in the unfinished portion of my basement. I would say both were well designed. Both were exceptionally loud and messy. Salt spray was crazy and it becomes a little difficult to monitor water levels for top off with a surge. I would not have put one of these in the finished portion of my basement, let alone a mian display. From the basement, I could hear it in my bedroom.
I loved the corals reaction to this method. I wish I was able to make it work. IMHO, it's an amazing flow option. But, I'm going to tell you the same thing I told Eric... too loud, too messy and float switches for ATO are out of the question.