DIY Fitting a P-Trap to a Sink

1). Locate the threaded portion of the sink strainer basket. The sink strainer basket is the drain hole that slides through the sink basin's opening and protrudes into the under-sink cabinet. Twist the strainer's nut counterclockwise to loosen and remove the nut. Remove the washer from within the nut and place the washer into the flat-rimmed opening of the tailpiece pipe.
2). Slide the strainer nut over the smooth side of the tailpiece, threads facing up. Press the flat-rimmed side of the tailpiece against the strainer. Slide the nut up the tailpiece and against the underside of the tailpiece's rim. Engage the nut with the strainer and turn clockwise to tighten the nut and join the tailpiece to the strainer.
3). Twist the nut attached to the tall side of the trap counterclockwise. Loosen and remove the nut from the trap. Remove the washer from within the nut. Slide the nut, threads facing down, over the open end of the tailpiece. Slide the washer, tapered side down, onto the open end of the tailpiece.
4). Slip the tall side of the P-trap over the open end of the tailpiece and press both the washer and nut against the P-trap's threads. Twist the nut clockwise to engage trap's threads and tighten the nut.
5). Remove the nut and washer from the remaining short side of the trap. Slide the nut over the straight side of the extension pipe with the nut's threads facing toward the opposite, curved end of the pipe. Press the washer, tapered end down, onto the curved end of the pipe until the washer butts against the rim near the pipe's edge.
6). Press the curved end of the extension pipe into the open end of the P-trap until the washer seats within the P-trap's opening. Slide the nut toward the P-trap's threads. Engage the nut with the P-traps threads and twist clockwise to tighten.
7). Twist the entire assembly to align the extension pipe with the wall drain. Attach the extension pipe to the wall drain, using a compression nut or solvent-welded adapter fitting. After connecting the extension pipe to the wall drain, return to each nut and tighten one quarter turn past hand tight. Run water through the drainpipes and check for leaks.