This kit is normally included with the purchase of a HOG. The air vent allows air in the HOG tank to escape as it fills with rainwater. With proper ventilation, as provided by the air vent, water will flow from the tank in a strong, smooth stream. Be sure to install the top portion of the vent above the lowest portion of your gutter overflow, otherwise water will spill out of the vent when the system is completely full.
If you have more than one HOG installed, connect your modular HOG system with threaded connectors. The connectors, which conduit the water between tanks, enable each tank in the system to fill simultaneously with an equal level of water.