When making beer using whole grains, you need a way to get the sugars out of your malt and into your beer. All you do is use a sparging bag to line your bottling bucket (with spigot). Pour in your mash, follow with hot water, and start your boil.
A necessity for those who will be making their first 5 gallon batch of all-grain beer.
Note: This is for 5 Gallon Brewing. For 1 Gallon, a strainer works best.