I'm getting ready to begin developing my film at home (mainly 4x5). My question is, how do I safely dispose of fixer, mainly, and if there are any other chemicals (in the developing process only) that I should also be concerned about their proper disposal. I ask this because the place where I have been developing film until now, they also don't allow people to dump the water you use to wash away the remaining fixer. This also goes in a special container, and they also don't allow people to dump the washing agent down the drain. This also gets collected in the receptacle where the water used to wash away the fixer goes.

Anyway, how do I properly dispose of fixer? And is fixer the only chemical I should worry about or is there anything else?