Product review (5 stars): You Need The Rubber Gasket!
This is the first reply water filter I have bought that has an extra little rubber gasket. Mine was not attached, and I couldn't determine if I needed it. Since my water filters have never had that before, I installed it without it. The water was not coming out correctly, even after running several gallons of water as you do with a new filter, so I put the rubber gasket back in and it worked great.