The best salt to use is coarse Kosher -- also called the "pinchable" salt
It's larger than table salt but smaller than rock salt. Rock salt is too big to get into cracks and table salt is too small to be genuinely useful. If you want it to smell like the stuff you buy at the store, add some orange oil.
A neato trick for cleaning downstems, etc. After rinsing with hot water, fill the entire cavity to the top with coarse Kosher salt. Slowly, SLOWLY trickle your alcohol through the top. You should see the wet-line move down through the piece, getting darker as it collects resin. What's happening here is when the salt gets wet, it compacts and scrapes and is super-effective at removing resin. When you have alcohol dripping out of the bottom, you can clear the chamber and do your regular shake to clean the rest.
If your piece is super dirty, like you've had it a year and never thought to clean it, it's going to take more to do a good job. You can either go to town with an array of Q-tips and strangely-bent paperclips or let the whole piece soak in alcohol for about a week. My neighbor swears by that one. "Man, I've got so many pipes and I never clean 'em, when they get dirty I'm like 'Fuck it,' and I just go buy another one." but then he ran out of money, dunked the collection for a week and said they were like new.
