I use a tumbler like this one with corm media: http://www.cabelas.com/product/Cabelas-Model-400-Vibratory-Case-Tumbler/731767.uts?Ntk=AllProducts&searchPath=%2Fcatalog%2Fsearch.cmd%3Fform_state%3DsearchForm%26N%3D0%26fsch%3Dtrue%26Ntk%3DAllProducts%26Ntt%3Dtumbler%26WTz_l%3DHeader%253BSearch-All%2BProducts&Ntt=tumbler&WTz_l=Header%3BSearch-All+Products
Soaking in white vinegar also works or you can also try this stuff: http://www.evapo-rust.com/