Propylene glycol is used as a less environmentally-toxic antifreeze. It is not harmless; it is just less toxic than ethylene glycol used in most antifreeze. Finding a safe disposal method for propylene glycol can present a difficult task. The best solution is to reuse it, if possible. If this is not possible, then find a facility that will accept the waste and handle its disposal or recycling. Improper disposal of propylene glycol will contaminate groundwater, aquifers and cause problems in municipal water facilities.
Dispose of unused propylene glycol by using it in your vehicle or home cooling system, if possible. This is the safest method of disposal because it keeps it out of the environment and within a closed system. If you can't use it, offer it to friends or family who may have a use for it.
Dilute the propylene glycol and pour it down the sewer. If you live on a septic system, never pour the propylene glycol down your drain. It will damage the bacteria in your system and in the ground. It will filter from the drainage field into the groundwater and aquifer becoming a health risk for animals and people. Only pour it into a municipal sewer after calling your waste water treatment facility and inquire if you can dispose of a small amount in this manner. Some treatment facilities can handle small amounts of propylene glycol, while others can't tolerate any.
Seek out a service station or automotive parts store that will accept waste propylene glycol for disposal. It is likely that there will be a small charge for them to accept and dispose of it properly. They will probably send it to a recycling facility to recover and reprocess it for sale and use by other consumers.
Contact your local waste disposal company and find out if they offer a household hazardous waste collection site. Many larger communities run hazardous waste collection sites to protect the public water supply. Many of these facilities are free of charge.
never pour the propylene glycol down the drain into a septic system.