This mod is done to add a little more sound from the exhaust and to reduce back pressure. Many folks aren't satisfied with the sound this produces and the mod cannot be reversed. Another, but more expensive solution, is to retrofit Classic right footpeg brackets and Vulcan Classic pipes.
Make sure you have new crush gaskets for the exhaust, completely remove the Drifter exhaust.
The Drifters bladder has three external pipes, two 1 1/2" and one 1 7/8". Of the three, the two that are above each other on the bladders right hand side (as sitting on the bike) have 9 1/2" perforated tubes inside them. These two tubes just need to be hammered and chiseled, or a large screw driver will do to free them around their mounting locations, along with a few little tabs that hold them in place. (See Drawing For Clarification) Once this is done, they can be removed from the third opening that leads out to the back exhaust pipe!
That's it, the bladder is gutted! Your done no cutting open or welding it back shut! Just bolt it back on, re-install the stock Drifter pipe.