1
general::
Also, hash out. Discuss carefully, review, as in Let's hash over these plans again, or The department was hashing out the new syllabus. This idiom uses the verb hash in the sense of "cut into small pieces," a usage dating from the mid-1700s.
American Heritage Idioms
2
general::
Phrase(s): hash something over (with someone)
Fig. to discuss something with someone. • I need to hash this matter over with you. • I’ve hashed over this business enough.
McGrawhill's American Idioms And Phrasal Verbs