Description OPW 71SO-410C Vapor-Tight Overfill Valve, 10FT Bury, 10FT Tank The CARB-certified OPW 71SO vapor-tight 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. Retrofits directly for both new and existing tanks with 4IN fill risers. *This item is not eligible for free shipping.