Brake clean, spray choke cleaner, ect. Just make sure to either blow or wipe them out afterwards to remove the residue if any left. Then if you live in a moist area you may want to give a light coat of oil or sheath to prevent rust. The q-tips soaked in alcohol or Hopps work great too. Just don't want a bunch of oil in a bottle neck sizer die. Hoppes leaves a bit of a oily film that should help with rust.