Can't move items to Trash – resistant to usual fixes On an internal data-only SATA HD, the OS forces me to delete files immediately, just as for removable media, a mounted network volume, or any unwritable volume. 

Already tried removing and recreating the .Trashes directory, etc. 

The error message is familiar: 


  Are you sure you want to delete “filename.ext”?
  This item will be deleted immediately. You can’t undo this action.


I am working in the 501 account, the primary admin. 

From the volume root, the permissions settings I see are: 


  drwxrwxrwx     root  admin    .Trashes


And for the Trash subdirectory belonging to the user account, it's also: 


  drwxrwxrwx     root  admin     501


Writes are not getting denied by extended permissions (because there aren't any). 

The drive is seen by the System as a generic internal journaled SATA HD that's writable, repairable, not ejectable, and not bootable. No problems found with file structures on the volume.  Already recreated the Finder's plist file for luck. 

I can live with the behavior, but it interferes with file de-duplication apps among other things. What am I not thinking of? 

Trash on the System disk works as expected. OS X El Capitan v. 10.11.6 (desktop OS, no OS X server).



Thanks for the pointer to https://apple.stackexchange.com/questions/249328/trash-folder-not-a-directory-files-only-delete-immediately but I've got a different situation. 

The earlier question was about a .Trash folder inside the users' Home directory on a startup volume. Other local volumes have a different file architecture, and the OS manages them differently by design. 

The answers don't apply either, because the OP's temporary fix does not make a difference for me, and in my case the required attributes for the .Trashes and 501 directories are not getting removed. Those look fine on inspection, although the Trash folder on that volume doesn't function.
Filesystem errors that bedevil daily use... grrr... I had something similar to that and nothing I did: repairing the disk, using DiskWarrior and some of the tricks you tried, did a thing.

Finally I got fed up and backed up the drive, deleted the partition and recreated it and reformatted it. Problem went away. If you asked me what caused it I couldn't tell you, but backing up a drive that was basically an internal backup drive so I could re-partiton was almost as annoying as living with the problem.