Stock exhaust question

[on2wheels52]

While i had the exhaust off for a tire change it seemed a good time to file down some of the scratches and wire brush the thing off for coat of header paint. I noticed a small sheet metal screw in the pipe just in front of the muffler. I was curious as to its purpose.
While on the exhaust subject, is there a method of 'de-carbonizing' the muffler or is it unnecessary on this model?
Jim

[mikal]

The most effective method I have heard of for cleaning the pipe is to take it to a radiator shop and have it dipped there.
I have never had a pipe long enough to have it cleaned.