I have been told it was ok in a sanitary sewer in our municipality, such as a toilet or basement floor drain (if you know it connects to the sanitary sewer collection system, though many don’t) as it will be treated. NEVER a stormdrain or catch basin in the street as that will be an environmental big no no. It will go untreated into fresh water systems. Many places offer hazardous waste disposal programs including antifreeze, please check out options and follow any local recommendations.