I wanted to share a method I use to clean my carboys. I generally only soak (dilute bleach vinegar water solution) then give a quick pass with my carboy brush. Very effective in my experience.
But if you have some stubborn stains, try mixing a few ozs (depends on carboy size 5 ozs for a 6.5 gal works for me) of rubbing alcohol and some salt. The salt will not dissolve in the alcohol and acts as a liquid sandpaper of sorts. Bung the carboy and roll and/or shake. Gets the glass very clean. Will not scratch the glass in any way, regardless of my analogy.
For added economy, the solution can be transferred to another carboy or storage vessel. Can be reused (as a cleaner, not a sanitizer) for quite a long time.
The alcohol can react with plastic, so I cant say if it will work without hazing the plastic, but for glasss, its a champ.