This is an accessory you can use to connect multiple closed bases into a larger capacity reservoir. That way you do not need to care about plumbing and providing an external reservoir. It makes sense to combine the liquid reservoir for >3 standalone vertical barrels if you like to run all of them with only 1 pump drawing nutrient solution from only one master base. You can find an example on our integration page. Since the other bases are connected into a circle, liquid will be provided to the master base. Using the valves enables you to isolate any vertical barrel any time for cleaning.