I have found that the best way to reduce staining from clear aligners is to maintain a good level of oral hygiene. This prevents the aligners from becoming stained in the first place. Also advising the patient of good compliance will help reduce staining as they can progress through aligners quickly without having to hold or backtrack, preventing prolonged wear and increased staining.
However if the patient raises the concern of their aligners becoming stained I usually recommend 50% warm water 50% household white vinegar and a gentle brush. BD