#1 Check Assembly 6" 375AST/375ASTDA/475ST/475STDA
Manufacturer: Wilkins
Size: 6 Inch
Product model: 375AST, 375ASTDA, 475ST, 475STDA
Lead Free: true
Size: 6 Inch
Product model: 375AST, 375ASTDA, 475ST, 475STDA
Lead Free: true
https://www.youtube.com/embed/3d2rNoroZ_c Specification Sheet Repair Parts Guide Relief Valve Discharge Rates 
Zurn Wilkins Backflow Prevention 375 (4 inch & 6 inch) - How to Repair
Zurn Wilkins Backflow Prevention 375AST - How to Maintain
Zurn Wilkins Backflow Prevention - How to Troubleshoot Relief Valve Discharge