How to properly dispose of old coolant?

Ya, you can wait for hours in your car behind tree huggers at your local hazardous waste rodeo in town, BUT here's how we start new trends that don't harm anyone or waste gasoline. 

Keep it in the used coolant containers marked, "Used Coolant!" and when you find yourself in knee deep ice and or snow during the winter, you can pour a little bit on your driveway and side walk, a little goes a long way, and it will keep the surface from icing up and it will not chew up your concrete the way salt does. It evaporates the same as most liquids when exposed to fresh air and sunshine. 

The town I live in has a hazardous waste collection site where they take items like old paint, antifreeze, and household chemicals. Maybe your city has something like that?

Here is what you should do. Contact local recycling centres or check their websites to find out whether they recycle engine coolant. If they don't, they should direct you to your nearest drop-off point. Some garages will also accept old coolant. Recycle your coolant in a well-sealed container that is clearly labelled.

Not the drain. Considering it is lifelong coolant I never remove it.    But you did, FOOL.  I would dig a hole in the back yard and pour it down the hole and then plant the dirt back over what is mainly water.  The dirt on top will grow lawn again and that is that.   It will take EONS to reach the water table which is 30 feet down in the ground.  DINOSAURS will rule the earth again.  Or the earth will be enveloped by a super sized sun on its last days and the planet gets vaporized.  

..You know, = the future.

Of course. That's the law. If they sell the fluid, they have to take back the old. Environmental laws.

You call the people who deal with them almost every day, a garage.  Think inside the box.

I take mine to my local recycle center

Where I live they do not have a place to dispose of old oil or antifreeze. I tried to get them make a place to depose of such things and nothing has ever happened over the years. So guess what, most of it goes to the landfill. Not the right thing to do but we have to get rid of it. But don't dispose of it down the drain.

It's illegal to pour it down the drain. Many auto shops recycle antifreeze. The city I live in has a yard waste site that also accepts drain oil and antifreeze.

No. That pollutes water courses. Google 'antifreeze disposal' for your area.