I've read in my manual that the carbon in the muffler should be occasionally purged. I can't seem to get the dang plug out of the bottom of the muffler. I've tried everything---wrenches, sockets, vice grips, even a pipe wrench---but I can't seem to get a good hold on it. I think the plug is made of brass and it just seems to keep stripping. How important is purging the muffler?

 

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