Yeah, mine is flat, not beveled. I guess I just meant that the arrangement of components in that picture reminded me of my solution - my gasket/washer is shaped differently, though, you're right.

That's why I didn't even think to slide it over the neck. Even when I tried it I was worried it would tear. But, the material is pretty strong (I had to remove and attach it a couple of times because of wrong order of events) and it really snugs in tight. So, even though it's flat and thin I think it's the ticket.