Identify the components of the compression fitting. The compression seat is the portion of the pipe to which the fitting attaches. The compression nut is the portion of the inlet tube that screws onto the compression seat. At the end of the tubing is a circular piece called a compression ring.
Wrap the male threads of the compression seat with plumber's tape, sometimes referred to as "thread tape."
Insert the inlet tube into the center of the compression seat.
Slide the compression nut over the compression seat until the female threads of the nut begin to overlap the male threads of the seat.
Hand-tighten the compression nut onto the compression seat.
Tighten the compression nut with a wrench or, if the inlet tube is made of copper, with a flare-nut wrench to complete the process. Copper tubing can easily be bent, particularly if the compression nut is tightened with a standard wrench. A flare-nut wrench evenly distributes the force applied by the wrench around the nut, which minimizes the chance of bending the copper tube.