Where do you discard chain cleaning solvents/degreasers?
Disposing of hydrocarbon-based solvent would have to be at your local waste disposal service. Where I live, you can drop it off at the same place that you drop off bottles and cans (we pay an environmental refundable deposit). I suppose you could also burn it off, but that also seems environmentally harmful.
Flushing used citrus cleaner down the drain shouldn’t be a problem. Assuming where you live has a robust wastewater treatment system in place, I don’t see how it is any different from disposing of, say, oily dishwater. I suppose you could drop it off at the disposal centre too.