I got a DEP. its just fibreglass mate... well, wadding, but you know what i mean... eer, you can gut it but itll be stupidly loud mate, and the fact that the tube inside is like a mesh, will probably disrupt the air flow... because im sure its made too be a straight-through pipe. There isnt really a way too clean it if im honest, and tbh, its only the bit around the mesh tube that is black, the rest is fine.
I personally wouldnt gut it... the best thing too do if you want it too sound and look better, is send it off too bradders... he'll do an ace job of sorting it out for yer mate. :)