You're mixing up two things. In Trash, neither the pointers to the data, nor the actual data is deleted, they're just marked as deleted by moving them to a folder called Trash, or appending .trashed to their file name, which the file management part of the OS treats as trashed. If you clear your Trash, or directly delete the file permanently, the pointers are deleted so any data on the disk is marked as free to be overwritten, but until something actually overwrites it, you can recover it using data recovery software. If you change all the physical bits on the disk then the data is permanently deleted and can't be recovered. Unless, of course, it was copied to someone else's server first.