All used solvents, thinners and reducers are hazardous wastes. There are only two legal ways to dispose of these hazardous wastes:
Hazardous waste generators have a “cradle to grave” responsibility for safe disposal of hazardous wastes. Federal law says the generator is responsible for the waste he creates, regardless of who hauls it away or where it is stored. His name is on the barrel and if it is spilled or otherwise causes pollution, he is responsible for the cleanup. Forever!
Of course to dispose of hazardous wastes in any unlawful way is just foolhardy and a good way to risk heavy cleanup cost, stiff fines and possible jail time.