Description OPW 71SO-4010 Non Vapor-Tight Overfill Valve, 10 Ft. Bury, 10 ft. Tank The CARB-certified OPW 71SO Overfill Prevention Valve is designed to prevent the overfill of underground storage tanks by providing a positive shut-off of product delivery. The shut-off valve is an integral part of the drop tube used for gravity filling. The OPW 71SO allows easy installation (without breaking concrete) and requires no special manholes. *This item is not eligible for free shipping.