You have a Suburban. The white tube goes to the cold inlet. There is a Black tube connected to the HOT outlet. IF you remove the back water cold input line and the nipple, IF the White input is still there you are OK as Suburban will sometime push one in too far at manufacture and they leave it in there and install another one. IF this is the case, you can shine a light thru the anode rod hole and see if a 2nd was installed, IF NOT, you remove the input water line and the nipple and slide the one in and have it POINT DOWN. when you get it in just use the palm of your hand to gently drive it in flush and then reinstall the threaded nipple and water line. The purpose is to direct the cold water DOWN to prevent uneven mixing of cold and hot. Doug