The skimmer box works by removing the main tank's surface water through a slotted overflow compartment. From there the water travels through a large siphon into a second box that hangs behind the tank. This second box is divided into two compartments; the siphon opens into one of them, and the water overflows from there into the other compartment, and then from there it drains into the sump. The two compartments in the second box keep the siphon from losing water when the main pump is turned off.

A high water flow through the skimmer box keeps air bubbles from collecting in the siphon tube. The tube also needs to be cleaned periodically, because algae growing inside it will impede water flow.

The return pipe from the sump has a small hole drilled in it to allow air to enter the pipe whenever the main pump is turned off. This prevents the return pipe from siphoning all the main tank's water back into the sump.

The overflow box used to produce quite a bit of noise due to the air that gets sucked into the pipe leading to the sump. The noise was considerably reduced by adding a PVC silencer designed by Ken Stockman. Instructions on how to make this silencer can be found at http://home.att.net/~rstockman/overflow.htm .