See the text boxes for where to put sealant. I added some sealant at the top end of the threaded portion, too. The design of this pop-up assembly could allow leakage because the flange fits on the outside rather than on the inside of the body. Insert the body into the hole in the sink from below the sink. Screw the body onto the finished flange without disturbinng the finished flange and its seal. Hold the body of the pop-up assembly so the fitting for the linkage points toward the rear of the sink, that is, the side toward the wall.