First all welcome to the boards.
You are definitely starting off the right way by asking questions BEFORE you set up your tank.
Now to let you in on a little behind the scenes knowledge of the board, T3 is a good guy, but he is from the backwookds country. So the bulk of his mechanical knowledge is about stills for making moonshine and squirrel rifles for huntin' vittles.
To me that looks like someones idea for cutting down on the gurgling noise that overflows can make. It also looks pretty dangerous to me. I don't like anything that can get stuck and mess with the flow of an overflow. The second tube looks like some type of suction break or some way of letting air in to reduce the flushing noise overflows can sometimes make. I would recommend 3 things. 1, Do NOT install that disc thing, there is no real reason for it. Thousands of overflows are working without that decive. 2, set up your overflow with a couple of rectangular trash cans and try things out for yourself. That way you can see how things work and try that disc thing. 3, Ask about this in the equipment section. SCSI hangs out there and may know more about this than me.
HTH
Scott