It is a flat rubber gasket and is held in place by a metal ring that has high ridges on it. I don't know their purpose. The fingers that hold it in place are metal and somewhat of a spoon shape. When I reassembled I wasn't sure if the fingers should go between the ridges or on top of them. I did the between but now I am wondering if the inverted spoons should go on top of the ridges vs. what I did. I can't find any pictures of this install. This is also a poly tank using their parts but again it never leaked before when I did it a second time. I definitely will have to do it over again but this time, I want to eliminate any doubt. Thanks.