I'm new to Buffalo NAS but here's one thing I found to fast delete many files (like trashbox) :
1. create a new shared folder, say 'tmp', to use with sftp
2. enable sftp for all shared folders from which you want to delete fodlers / files
3. use WinSCP to connect to the NAS
4. find each folder you want deleted, right click, 'move to', then select the 'tmp' folder as destination
5. when all folders are moved to the tmp share, connect to the admin web, and click 'delete share'
the web interface takes a few seconds to report 'Done', but you can hear the NAS work for much longer - a couple minutes for a few dozen gigs in 20.000 files on my LS-WV 4TB
if the 'empty recycle bins' feaure doesn't work, this trick should give you a work-around.
