I recall this causing a major argument years ago on this board, but the official policy in many communities is still you just dilute it heavily and pour it down the drain. Even if you take it to a recycling center, that’s usually more or less what they do to it. Part of the reason why there aren’t as many places that take used antifreeze is that the EPA doesn’t technically consider it hazardous waste. The main hazard is animals drinking it, but this has more to do with it’s sweet taste which encourages them to drink it in large quantities as opposed to it being spectacularly poisonous.
You need to call your local sewer utility before you do this because the amount you can pour down per day and how much you should dilute it depends on what kind of waste water treatment they’re using, but you generally want to dilute it at 3:1 (assuming the coolant itself is already a 50:50 mix) and you can do no more than 10 gallons a day. Also, you definitely do not want to do this if you have a septic tank as it will kill the little microorganisms that treat your waste.