As long as you dilute the chemistry and flush after dumping with water, there is no trouble with typical photo chemistry. You should use some form of silver recovery to avoid putting the silver in the waste stream.(posted 8917 days ago)Porter's (www.porters.com) carries an electrolytic silver recovery setup for about $35 called the "Silver Magnet." This allows recovery of the silver and the company will pay you for the silver.
For cheaper, just throw steel wool into the fixer. Let stand (agitation will help) and discard the liquid. Dry the resulting material and dispose of properly.
The reason for dilution and flushing is to make sure that no corrosive materials end up standing in your system. In most cases there is no problem. But some systems could be damaged by the pH of some photo chemistry over time.