At its most fundamental level, a refugium is nothing more than a safe place where some livestock can grow free from the reach of its would-be predators. It can be a section of an aquarium separated by a simple divider, a drop-in in-tank refugium, a section of a sump or a separate tank tied into the main system. The purpose of the refugium in an aquarium is to allow certain species to grow or reproduce.
While this basic concept is implemented in all refugia, most have developed to serve more functions. While specific refugium functions are many -- including denitrification, nutrient absorption, algae cultivation, invert cultivation, coral propagation, alkalinity buffering, ph control, calcium supplementation and detritus filtration -- most refugia are designed with one of two (or both) functions in mind: filtration or feeding.
You can build one out of a spare tank or one bought just for this, any size you want. Bang Guy has a 900 gallon fuge that he calls a lagoon. (barbie sold seperatly)
Plumbing it depends on how you want to set it up. As part of the main display, hidden away underneath, above your aquarium, in a seperate room, hang on back, many possibilities.
By placing macro algea inside you can have your nitrate reduction as well as a DSB for further NO3 reduction. Using partitions you can place your pump inside to return to the main and keep your pump out of the sandbed or macro algea's. If succesful enough you may no longer need a skimmer or other machanical filtrations.
Thomas