The system is very simple. I have 4" of Aragonite sand in the carrier. There is about 2 cups of coarse river stones on the top. Six 3/8" holes are drilled at the top of one side of the carrier on a downward angle. The carrier sits perfectly on the top lip of my tank (a happy accident). One of the Aquaclear units drains directly into the carrier, and the water then exits from the drain holes. Note, that the feed pipe for the Aquaclear had to be extended with 0.75" tubing to allow it to be curved around the side of the carrier. Also, there is a small length of 0.75" tubing on the input tube as it sits in the Aquaclear -- this allows me to position it when starting to prime the filter. The lid (not shown) is trimmed to allow covering the refugium to minimize water evaporation.
Pictures show the unit in operation as well as the draining action.