In this video, This Old House plumbing and heating expert Richard Trethewey re-plumbs a poorly draining sink.
1. Remove the garbage disposer and disconnect all the old traps and drain lines from beneath the sink.
2. Use PVC primer and cement to glue a solid plug over the end of one drainpipe stub out. Glue a threaded clean-out plug onto the end of another stub out.
3. Find the dishwasher connection on the side of the garbage disposer. Use a screwdriver to remove the knockout plug from the disposer. Now reinstall the garbage disposer to the sink.
4. Attach a PVC disposer elbow to the garbage disposer and install a new PVC trap and drainpipe to the stub out in the wall.
5. Connect the disposer elbow to the new trap with a PVC T-fitting. If the fitting is too long, cut it to length with a PVC tubing cutter.
6. Attach the strainer and PVC tailpiece to the drain hole in the sink.
7. Hold the PVC waste arm in place so that it spans from the tailpiece to the T-fitting on the garbage disposer.
8. Mark a cut line on the end of the waste arm at the T-fitting. Also mark a cut line on the tailpiece. Cut both the waste arm and tailpiece with the PVC tubing cutter.
9. Install the waste arm and tighten the threaded fittings to connect the arm to the tailpiece and to the T-fitting.
10. Attach the dishwasher's discharge hose to the disposer with two stainless-steel hose clamps. Tighten the clamps with a screwdriver.
11. Turn on the kitchen faucet and let the water run. Be sure the sink is draining properly, then check below for leaks.