I just purchased an Hoya PL-CIR filter off craiglists (I'm starting photography and it was cheap) and it looks like there is some dust/dirt between the two lenses.
Is there a way to safely disassemble it so I can clean in between ?
Short answer: No.
Long answer: If you had the time, equipment, and experience; yes. You could disassemble the layers and rebond them with some varying degree of success.
What you see might not even be dust/dirt. Layers of the filter material may have become de-laminated due to the bond between the layers becoming dissolved by the "cleaning" solution. A thin air layer between the plates may be the problem. It would not appear so transparent without the optical cement bonding the layers.
Moral: don't soak/dip/immerse lenses or filters in solutions. Use cleaning materials approved for photographic optics in accordance with the instructions. sparingly
Joke: Safe way: Use heavy gloves so you won't hurt yourself if the filter breaks.
Quote: "The bitterness of poor quality remains long after the sweetness of low cost has been forgotten."