Cured solid resin can be disposed of in the trash.
WARNING When handling resin wear protective gloves/protective clothing/eye protection/face protection
Uncured liquid resin must be disposed of according to local regulations. In some jurisdictions, e.g., California, it is classified as hazardous waste. Contact your local municipal waste system for guidance on proper disposal.
UNDER NO CIRCUMSTANCES SHOULD LIQUID RESIN BE DUMPED DOWN THE DRAIN OR SINK.
If you cure liquid resin before disposal you can dispose of it in the trash. To do this, pour the resin into a transparent plastic bag and leave it out in the sun for a week or so. Exposure to the sunlight will cure and harden the resin, at which point, you can safely dispose of it in the trash.