King of the Hill: Season 5, Episode 17

5 - 17: It's Not Easy Being Green

Bobby takes up a new interest in environmental issues, provoked by a new teacher. When the cause rallies to drain the quarry, and rid it of all waste, Hank is dead set against it. Years earlier, while in high school, the gang wrecked Boomhauers car, and pushed it into the quarry, pleading ignorance. Bobby finds out, and lets Boomhauer in on the secret, just before they pull out 'Ol Betsy', to his horror.