The Knight Injection Back Check Valve p/n 7901350 is used to inject a variety of chemicals into the water line.
This injecton valve has a 1/4" OD Tube Connection and an 1/8" NPT Pipe Connection.
The Duck Bill is made from Viton material which lasts longer than other elastomers.
Duck Bill is Replaceable. See item number 0300437:Knight Replacement Duck Bill, Viton