Y-Valve. The Jabsco Y-Valve is designed to provide flexibility of onboard waste management by diverting waste either into an onboard holding tank or directly overboard where legal to do so. Check local and Federal regulations to determine where direct overboard discharge of untreated waste is permitted. No overboard discharge of untreated waste is allowed within three miles of shore.. Some near shore areas and inland areas are designated as "No-Discharge Zones" where the discharge of any onboard