Aprilaire Feed Tube 4335. This is the water feed tube inside the humidifier, which connects the solenoid valve and then to the water distribution tray at the top of the unit. For use with Models 400, 400A, 400M, 500, 500A, 500M, 600, 600A and 600M. Also fits Lennox Model WB3-17, WB317. Feed Tube includes: orifice, in-line strainer, compression nut and plastic ferrule.