How to Install Pipes Under a Double Kitchen Sink

Dishwasher hoses connect to branch tailpiece pipes.

The presence or absence of under-sink appliances determines the design of a double sink's drain assembly. Because dishwashers and garbage disposals drain through the sink's piping system, you must choose a drain assembly that accommodates your appliances. A sink without appliances requires an end-outlet or center-outlet continuous waste assembly. End-outlets plumb double sinks where the main drain aligns with one basin. Center-outlets plumb double sinks where the main drain sits between the basins. Variations of these drain assemblies allow space for garbage disposals and provide inlets for dishwasher drain hoses.

Things You'll Need

• End-outlet or center-outlet continuous waste kit
• Tape measure
• Pencil
• Emery cloth
• Rag

Instructions

1. Remove the tailpieces from the continuous waste kit. Twist the nuts attached to the sink basins' strainers counterclockwise to loose. Remove the strainer nuts and accompanying washers. Place the strainers' washers into the flange-end of the tailpieces.

2. Feed the strainer nut onto the arms or tailpieces with threads facing up. Press the flanges against the strainers' openings and slide the nut against the strainers' threads. Twist the nut clockwise to thread the tailpieces onto the strainers. Tighten one-quarter turn past hand tight.

3. Measure the distance between the tailpieces' bottom openings with a tape measure if you are installing a center-outlet kit. Subtract the width of the center-outlet's tee from the measurement. Add roughly 1 to 2 inches to accommodate the length that the tailpieces must enter the tee.

4. Divide the result by two to determine the overall length of a single center-outlet tailpiece arm. Mark the dimension on the center-outlet tailpiece arms with a pencil; you must cut from the smooth end of the arms. Cut the arms to size with a hack saw. Clean burrs from the cut ends with emery cloth and a rag.

5. Slide a slip-joint nut and washer over each tailpiece. Align the arms' threaded ends with the tailpieces for a center outlet. For an end-outlet kit, align the tee with the basin strainer that sits above the main drain and the arm with the remaining basin. Slide the washers and nuts against the pipes' threads and twist clockwise to attach the pipes to the tailpieces. Tighten the nuts just shy of hand tight; you will need to twist the pipes later.

6. Slide a slip joint nut and washer over the smooth ends of the tailpiece arms for a center-outlet kit. Slide a nut and washer over the smooth end of the remaining arm for an end-outlet kit. Slide the center-outlet tee over one arm. Twist the remaining center outlet arm and slip it into the other side of the tee. For an end-outlet kit, simultaneously twist the tee and arm to slip the arm into the tee's side outlet.

7. Slide the slip-joint washers and nuts against the threads and turn clockwise to tighten. Feed a nut and washer over the smooth, bottom outlet of the end-outlet or center-outlet tee. Slip the remaining piece from the kit, a trap and extension pipe, onto the tee's smooth end. Slide the washer and nut against the trap's threads and turn clockwise to join the trap to the tee.

8. Feed a slip-joint nut and washer onto the trap's extension pipe. Twist the trap to align the extension pipe with the main drain. Slip the pipe into the main drain. Slide the washer and nut against the main drain inlet's threads. Turn the nut clockwise to connect the extension pipe to the main drain. Tighten all previous connection one-quarter turn past hand tight. Run water through the assembly and check the new connections for leaks.

Tips & Warnings

• If the trap's extension pipe is lower than the main drain inlet, measure the difference and trim from the smooth end of the end-outlet or center-outlet tee to alter the pipe's height.

• To install a dishwasher drain hose, substitute a branch tailpiece on one basin's tailpiece.

• For end-outlet assemblies, attach a garbage disposal opposite the basin that sits above the main drain.

References

• Fine Homebuilding: Installing a Kitchen Sink
• Keeney Manufacturing Company: Cast and Wrought Tees Installation Instructions
• Ace Hardware: Working with Plastic Pipe