1" NPT Plastic Adapter Tube, part number 7278442 ( or WS60X10013 ) with o-ring as shown.
The system REQUIRES Two of these, so order accordingly.
NOTE: This is for use IN PLACE OF ( not with ) the By Pass Valve 7129871, WS15X10012 625.34372
This is the white plastic adaptor tube that slides into the Standard Valve Body ( called 3/4" and valve body has 5 screws in valve cover, NOT to be confused with the Large 1" that has 8 screws for Valve cover / Valve body ), locks in with standard Clip ( 7116713 ), and gives you 1" male pipe thread to attach your plumbing pipes to at that point.
Also used with By Pass Valve 7278434, WS15X10053