Do a general cleaning and inspection and then decide. Once you get into the airway, you'll see if a pipe is clean, or as clean as it looks. For acrylic stems, a long soaking in dish detergent and pipe cleaner cleaning repeatedly should do most of them. Don't be afraid to flush out briar or Meerschaum chambers and shanks; they are all immersed in the process of carving and finishing anyway. SP does a respectable job of sanitizing, but I'd put any pipe through a general cleaning and inspection, and proceed as needed. Beginners should go easy with reamers; a lot of damage can be done with those. Likewise go easy with buffers, which can remove stamping and finish.
