There is a config setting regulating how often the validator will remove the "garbage", i.e. unused objects that it still stores but they are not really used but kept just in case (no connectivity to download updated records, broken manifests, CRLs, etc.). The setting is called "rpki.validator.rpki.object.cleanup.grace.duration" and by default it is set to "P7D", i.e. a period of 7 days, which is pretty conservative. You can set it to much smaller periods, 1-2 day or 12 hours and still have reasonable behaviour.
There is another parameter “rpki.validator.validation.run.cleanup.grace.duration" with the similar meaning, but it's less crucial when it comes to storage space.