It's currently not done as an ongoing process, but every so often there'll be an announcement of an upcoming clearing. tle="" target="_blank">Here is a link to the announcement from the most recent one, back in June.
"To qualify for clearing, an account must have been inactive for at least 7 years or have been banned for at least 6 months."
Usually, when the time comes for a clearing, all the eligible pets will be moved to a certain showroom so you see what is being cleared.