BackupPC does not have scripts or commands to actually remove backup from the pool. One day you will want to remove that and for that purpose you have to “hack” your way in.
Easiest way to delete backup for me was this way:
rm -fR <backup_number>
/usr/share/BackupPC/bin/BackupPC_nightly 0 255
After this, you will see space reclaimed and you can check it with
df, but you still need to remove statistic line, otherwise you will see it in your web interface. To do that:
ctrl+k you can remove the line with <backup_number>.
Relog to your web interface and voila! No more <backup_number>.