Yep, I could not resist. After Glider told me about the check valve, I had to tear a filter apart. Just like you said, a rubber disc that covers a series of outside holes along with a metal washer and heavy spring. That is 1 beautiful filter element also. I use to think the price for the filter was a little steep. Now after seeing what was inside I don't see how they can even make it for that price. It's a bargain.
