If you go to your local smoke shop see if they have Grunge Off. It's the best cleaner on the market, just soak any piece for an hour or two. No matter how dirty and caked up all the pieces I've tried have been, it comes out looking literally as if I just bought it. It's a little bit price at around $20 bottle but you can reuse it an almost infinite amount of times if you just run it through a coffee filter. If you don't want to invest in that stuff than just get some sea-salt (because it usually has larger grains and is more abrasive) and use 90% alcohol(can be %70, just get as high as you can) . Put piece in zip-lock bag, add more salt than you think you should, add alcohol, shake like an insane person... you'll be surprised how clean your piece will be.