Most coolants are safe to dump in the city sewer system. I'm not so sure about septic tanks though and I'm not gonna chance it. I just add a bunch of water to dilute it and dump it in the ground away from the well and garden.
Around here the quick change oil places will take it off your hands for you. The only ones that are safe in sewer systems are the propylene glycol based anti-freezes that are used for RV winterization. Sierra makes a PG anti-freeze for automotive use but you can probably say goodby to the warranty and the freeze point for a 50/50 mix is about 7 degrees higher(-27 vrs. -34).