The Hose Seal's purpose is to make a water tight / leak free connection between your Fill Hose and the rain barrel. Without the Hose Seal rain water will run down the side of your barrel as it is filling.
For one rain barrel, you will need one Hose Seal installed into the barrel to efficiently bring the rain from the FlexiFit Downspout Diverter, through the Fill Hose, and into the barrel.
Hole size is 1.5"
The Hose Seal is connected between #1 and #5 in the drawing below.