Used for attaching multiple barrels together with the linking fitting toward the bottom end of the barrel directly below the overflow fitting.
This allows you to modify only one downspout from the roof in any given location around the home or building and have increased storage capacity.
Simply remove the cap from the two linking fittings, thread the linking hose to the two linking fittings and the barrels are now joined. No tools required.
The barrel taking the water from the roof then shares with the rest of the barrels that are linked together with the linking hose. All barrels fill equally and then empty equally.
Some increase in pressure will be realized. However, the main advantage is increased capacity.