Final answer:
It is recommended to drain an oil filter for at least 24 hours before discarding to ensure environmental safety and adherence to disposal regulations.
Step-by-step explanation:
When discarding an oil filter, it is recommended to allow it to drain for a minimum of 24 hours. This duration is suggested to ensure as much used oil as possible is removed from the filter before disposal, which is beneficial for both environmental reasons and for complying with disposal regulations. The Environmental Protection Agency (EPA) provides guidelines for proper disposal, reflecting the importance of preventing oil contamination of the environment.