According to the EPA, spent fixer chemicals should be disposed of in the following manner:

picked up by a licensed hauler.
placed in a spillproof container and stored for future disposal in the office.
placed in a punctureproof container and placed in the regular trash.
sent down the lab sink following three minutes of hot water.

picked up by a licensed hauler.

Rationale: picked up by a licensed hauler – Spent or exhausted fixer can only be disposed of by a licensed hauler. That means that someone with the proper licensing to dispose of hazardous waste must come to your place of business and pick it up.