Where do I dump coolant?

Check with local dealerships or service stations. Many accept fluids from DIYs, some states make dealers and service shops accept all hazardous vehicle fluids. If you didn’t get the work done with them they can charge a nominal fee.

“On-site and off-site recycling are two choices available for managing used and acquiring recycled antifreeze. On-site recycling equipment can be leased or purchased through several California distributors. For a list of California companies that provide recycling services, see the California Integrated Waste Management Board’s (CIMWB) Household Hazardous Waste Web site; for equipment and supplies, please peruse the California Department of Toxic Substances Control’s (DTSC) Vehicle Service and Repair Program Equipment and Supplies Directory.

Recycled-content antifreeze can be purchased throughout California through distributors that recycle it. Vendors of both regular and extended-life recycled-content antifreeze can be found in the CIWMB’s Recycled-Content Product Directory.”

Read all about it here

Be careful with it. It’s sweet and highly toxic.

Thanks for being concerned about it. Take it to a ‘friendly’ service station, i.e. one that does oil changes and such.

Yes, to everyone elses answers, especially be careful that it is not left uncovered where a cat or dog might drink it.
A horrible way to die for pets, and it is especially very appealing to dogs.
I have a friend whose dog drank coolant and they saved him, the vet put him on an IV of Vodka which detoxes the poisons, a sick, drunk dog is a sad thing indeed. :-(