There is nothing complicated about it. You make a connection at the last hot water fixture connection and run a pipe back to the water heater. At the water heater, you install a valve, pump, hose faucet, check valve, and a second valve in that order and then connect to the drain valve at the bottom of the heater or into the cold water supply to the water heater. Plug the pump in and the hot water circulates. If it stops circulating and the pump is running, leave the water valve to the water heater open, close the second valve on the circ system, (the one closest to the water heater), connect a hose to the hose faucet and drain water until no air comes out. It will be easiest to determine if the end of the hose in immersed in a bucket of water while you are draining.