Couchbase data backup and removal of unwanted data

If we user couchbase along with sync_gatway, for live tracking. Then it will generate large data in Couchbase over a certain period of time.
Most of the data is useless after certain time, so how remove this unwanted data.

Do we need to use ‘Delete’ sql statement to delete these records.
Or we need to set ‘ttl’ for all unwanted records
Or there is any other mechanism (utility) provided by couchbase for this.

Any utility provided by couchbase for backup. (I mean not backup entire bucket but backup certain data from the bucket and remove the backed-up data from bucket.)

Looks like there is another thread that covers this. Have a look and/or reply there.