Go to an exhaust shop, have them flare the end of a piece of 2 1/2 inch pipe until it is 4 inches, and covers the large hole on the end of the honkers. leave about 1 inch of straight 2 1/2 on the other end.
When I say flare, you use a pipe flare tool on an end former that you would use to make a flare to accept a donut gasket, but just keep shoving the flare tool in till the 2 1/2 inch pipe is up to 4 inch, so it will be cone shaped.
Weld it on the end of the Honker. This not only gets rid of the soot, but makes the Honkers sound less chaotic. I have done this on 5 sets of Honkers so far, it works great.