Project Summary
- Duration of Work: 45 minutes to 2 hours
- Duration: 45 minutes to 2 hours
- Proficiency Level: Novice
- Projected Expense: Between $15 and $30
It’s uncommon for the drain assembly of a kitchen sink to malfunction and require repairs. However, when a sink is being swapped out as part of a kitchen renovation or upgrade, the installation of a new drain assembly for the new sink is typically included in the process.
The process of installing a sink drain can vary based on the differences between the new sink and the previous one, along with any additional components being added. For instance, if the new sink has a different depth, adjustments might be required for the branch drain pipe connection that goes into the wall. The installation can become a bit more complex if a garbage disposal is being added along with the new sink.
Prior to Starting
Kitchen drain traps come in a variety of bundled kits that include different configurations of components tailored to specific needs—some designed for single-basin sinks, others for double-basin sinks, and some for sinks equipped with garbage disposals. Kits made from both chromed copper and PVC plastic are offered, with plastic components being the preferred choice for most homeowners, as they are typically concealed from sight.
Typically, kitchen drains have a diameter of 1 1/2 inches, unlike the 1 1/4-inch pipes commonly used in bathroom sinks, so it’s important to ensure you select the correct size. In some cases, you might encounter a 2-inch kitchen drain outlet. If that happens, you can use adapter fittings to connect a 1 1/2-inch drain kit to the 2-inch outlet pipe.
While numerous drain trap kits come with flexible, ribbed tubing that simplifies installation, experienced plumbers typically avoid using them. The textured surface of the tubing can easily trap grease and food debris, leading to blockages. Instead, it is advisable to opt for smooth pipes, carefully cut to the appropriate length, to promote optimal drainage.
Tip
If you intend to swap out a conventional sink for a deeper basin sink, you might need to adjust the drain outlet in the wall to align with the new sink’s lower drain height. This adjustment is often necessary for extra-deep farmhouse-style apron sinks. Relocating a drain outlet is a complex task that is likely best handled by a professional plumber, unless you possess significant DIY skills.
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Requirements You’ll Need
Devices / Instruments
- Measuring tape
- Marker
- PVC pipe cutter or hand saw
- Channel lock pliers
Materials
- Kitchen sink trap assembly
- Drain and strainer unit for each sink basin.
Instructions
Verify the elevation of the drain outlet.
Before you take out the old sink and purchase a new kitchen sink, it’s wise to assess the height of the trap arm on the existing sink. The trap arm is the horizontal section that connects the U-shaped trap (the P-trap) to the branch drainpipe in the wall. It links to a sanitary tee fitting in the branch drain and should have a downward slope of approximately 1/4 inch for every foot to ensure proper drainage. To check the height, measure from the floor or the bottom of the cabinet to the center of the trap arm. If the height exceeds 16 inches, you might encounter issues with a new sink not providing the necessary downward slope for the trap arm.
Adjust the drain outlet downward if needed.
If you discover that the current drain outlet is positioned too high for the new sink’s depth, you (or a hired expert) will need to access the wall to reposition the sanitary tee that connects to the drain pipe. This task can be quite intricate, as it involves cutting through the back of the cabinet and the wall. For instance, the new sink installation did not provide enough space for a standard drain assembly to connect to the wall outlet (as shown in the left photo). Consequently, the sanitary tee that serves as the drain outlet has been repositioned lower (as depicted in the right photo). It’s important to ensure that the drain height allows for the trap to be easily removed and cleaned. If you need to lower the sanitary tee in the branch drain, it’s advisable to hold off on permanently securing the fittings until you have test-fitted the other drain components. Keeping the fittings loose will provide you with some flexibility for adjustments. Before moving on to the next steps, be sure to take out the old sink and place the new sink in the countertop. Our installation will feature a double-basin sink with a garbage disposal installed in the right basin.
Set up the waste disposal unit and the strainer.
Begin by positioning the garbage disposal on the chosen side of the sink, as it occupies the most room. After that, place a basket strainer in the other sink basin. This is also an opportune moment to set up any additional under-sink fixtures, like a water filter or a hot water dispenser. You’ll need to navigate around these installations while connecting the drain pipes.
Set up the drain tailpiece and the continuous waste pipe.
The drain tailpiece is a short vertical section of pipe that connects the sink strainer to a tee fitting. The tee fitting features a side outlet that accommodates the continuous waste pipe from the garbage disposal or the other sink basin, while the bottom outlet leads to the drain trap. Begin by temporarily attaching the tailpiece to the sink strainer using a slip nut and, if necessary, a slip washer. Next, connect the curved end of the continuous waste pipe to the drain outlet of the garbage disposal, again using a slip nut and washer. Ensure that the straight end of the pipe extends beyond the vertical tailpiece of the sink basin, maintaining a slight downward slope toward the tailpiece. Position the tee fitting against the tailpiece and waste pipe, and mark the cutting lines on both pipes where they will connect to the tee. Use a PVC tubing cutter or a hacksaw to cut the tailpiece and continuous waste pipe to the appropriate lengths. Reattach the tailpiece and continuous waste pipe, along with the tee fitting, ensuring that the connections are hand-tight. Adjust the components as needed, ensuring that the continuous waste arm has a slight downward angle toward the tee fitting. Finally, tighten the slip nuts a bit more using channel-type pliers, but avoid over-tightening to prevent damaging the plastic threads.
- Important: For sinks with a single basin, a tee fitting at the end of the tailpiece is unnecessary, as the tailpiece connects directly to the drain trap. In the case of a double-basin sink without a garbage disposal in either basin, the tee fitting is attached to the tailpiece of one basin, with the side outlet of the tee accommodating a continuous waste pipe from the other basin.
Attach the Drain Trap.
The assembly of the drain trap consists of a U-shaped trap bend and a J-shaped trap arm. The trap bend connects to the bottom of the tailpiece tee fitting, while the trap arm reaches into the drain outlet in the wall. Begin by loosely connecting the trap bend and trap arm using a slip nut and washer. Next, place a slip nut and washer onto the straight end of the trap arm. Insert the trap bend into the tee fitting on the tailpiece while simultaneously guiding the trap arm into the wall’s drain outlet. Adjust the trap components to ensure a direct route from the sink to the drain outlet, ensuring the trap arm has a slight downward slope towards the drain. If the trap arm is too long, mark and cut it to fit the space, then reassemble the P-trap. Use channel-type pliers to tighten all slip nuts, but be careful not to overtighten. Finally, ensure that the continuous waste pipe and trap arm slope gently downward towards the water flow, and verify that all drain connections are secure.
Tip
Ensure that the trap is oriented correctly, with the sharp curve positioned beneath the tailpiece. Although it might be appealing to rotate it the opposite direction to accommodate a tight area, doing so will prevent it from functioning correctly and could lead to leaks.
Inspect for any leaks.
Turn on the water in both sink basins and inspect each pipe joint for any leaks. If you find any leaks, tighten the connections. For a final check, fill each sink basin and allow them to drain quickly while you observe for leaks underneath. It’s fairly common for slip-nut joints to have minor leaks, which can often be resolved with a small adjustment. If the initial tightening doesn’t eliminate the leak, remove the nut, adjust the washer, and then re-tighten the nut, ensuring it is not cross-threaded.
