Q. How do you make antifreeze?
A. Take away her nightgown!
(In Michigan anyhow) Small quantities of household-generated mixed antifreeze can go down the drain so long as it's connected to the municipal wastewater treatment plant. Not into septic systems or storm drains.
Michigan hazardous waste laws classify a release of 1 lb or more of ethylene glycol to the ground, surface water, etc classified as a reportable release. Do the stoichiometry if you like, but municipal treatment systems can handle deminimis amounts of mixed antifreeze.
And as always, Check your local regulations.