That cotton filter bag is a totally-optional second stage filter for your Rumble Jar. And while only maybe 5% of our customers end up using them, those that do may want to give this method a shot to make it the straining process a whole lot easier. You basically tighten the bag using just the outer screw-on band from the Mason jar's lid, and then just pour into a new container. We'll let the pic do the talking, which came along with this pro-tip from one of our most creative Kickstarter backers.