For general cleaning, warm the chamber by entering Sesh Mode for one cycle. Unscrew the mouthpiece. Use a tightly wound cotton swab to remove remaining byproduct in the chamber and on the Dart. Wipe threading. Repeat if necessary.
It is normal for the bottom of your Plus chamber to blacken or darken over time, just as a ceramic nail typically would after some use. This should not in any way affect the overall performance of the chamber itself.
The mouthpiece, battery and threading can be cleaned by wiping with a cotton swab dipped in ISO. Do not soak any gunmetal parts of the Puffco Plus in rubbing alcohol.