FATSAC Check Valve and Adapter [W744]Check Valve and Adapter The FATSAC Check Valve and Adapter is a two part fitting that replaces the FATSAC Quick Twist Sac Thread Adapter that comes with ballast bags. The FATSAC Check Valve and Adapter is an optional upgrade for FATSAC ballast bags that replaces the standard Quick Twist Adapter. Just as easy to connect and disconnect as the standard fitting, the W744 Check Valve adapter also features an integrated check to prevent water from exiting