There aren’t many reasons for changing out the drain pipes under a kitchen sink, but one of the most common is during a kitchen renovation when the sink is being replaced. The steps for installing the sink drain will depend on how different the new sink is from the old one, as well as what other components are being installed. For example, in older homes, the new sink may be a different depth than the old one, so some alteration of the branch drain pipe fitting entering the wall may be necessary.
- Tools and Materials You Will Need
- Kitchen drain trap kit
- Tape measure
- PVC tubing cutter or hacksaw
- Plumber’s putty
- Channel-type pliers
Deep-basin sinks are very handy and stylish, but they take up more room beneath the countertop and may require that you lower the drain fitting in the wall to match the lower height of the sink drain. Before you buy a new kitchen sink, it is a good idea to check the height of the trap arm on the old sink, from the floor or base of the cabinet.
Measure up to the center of the trap arm. If the height is more than 16 inches, then you may find that a new sink will pose difficulties in achieving the necessary downward slope (grade) for the trap arm entering the drain fitting in the wall. This is especially true if the new sink will have deeper basins, or if you are installing a garbage disposal for the first time. If the measurement is 12 to 13 inches from floor to trap arm, then you are unlikely to have problems.
Knowing the height of the existing drain will prepare you for the possibility that you will need to lower the drain outlet in the wall as part of the drain hookup on a new sink.
If you find that the existing drain opening is not low enough to accommodate the depth of the new sink, you (or a professional) will need to open the wall and lower the position of the sanitary tee connecting to the branch drain. This can be a somewhat complicated job that requires cutting away the back of the cabinet and the wall surface.
In our example, the new deeper sink left insufficient room for connecting a standard drain assembly to the drain outlet in the wall (left photo). So, the sanitary tee fitting has been lowered (right photo). Keep in mind that the drain height needs to leave enough room to remove the trap and clean it out when necessary.
If you need to lower the sanitary tee in the branch drain, it is a good idea to wait until the other parts of the drain are test-fitted before gluing and securing the fittings permanently. Leaving the fittings loose will allow you some room for adjustment.
Before continuing to the next steps, install the new sink. In our example, we are installing a double-basin sink that will have a garbage disposal fitted to one basin.
Next, install the garbage disposal and basket strainer. Install the garbage disposal onto the desired side of the sink first, since this takes up the most space. On the other basin, install a basket strainer.
This is also a good time to install any other under-sink components such as a water filter or a hot water dispenser.
The continuous waste pipe is used with double-basin sinks to connect the two drain openings together before they feed into the drain trap. On sinks where one basin holds a garbage disposal, the arm of the continuous waste pipe connects to the outlet on the disposal.
Hold the continuous waste pipe up to the two drain ends and take a measurement for cutting the horizontal arm to the proper length. If you have a garbage disposal, this measurement will be between the sink strainer and the drain outlet on the disposal; if you have no disposal, just measure between the centers of the two drain openings. Do not underestimate the length, because the fittings need to be tight—you can always trim down the pipe if it is cut too long. Assemble the pieces in this order:
Install the vertical tailpiece onto the sink strainer first. Secure it with a slip nut slipped over the tailpiece and threaded onto the bottom of the sink strainer.
Slide a slip nut and beveled slip washer over the straight end of the continuous waste arm, then slide the end of the arm into the outlet on the drain tee fitting. Fit a slip nut and slip washer onto the garbage disposal waste outlet pipe, then fit the end of the outlet pipe down into the curved end of the continuous waste arm.
Adjust the pieces as necessary, making sure the continuous waste arm has a slight downward pitch toward the tee fitting. Secure the slip nuts with channel-type pliers. These do not need to be over-tight; the plastic threads can be damaged if you use too much force.
The drain trap consists of a U-shaped trap bend and a J-shaped trap arm. The U-shaped piece will fit onto the bottom of the vertical tailpiece, while the trap arm extends into the sanitary tee fitting at the wall.
Assemble the trap bend and trap arm together loosely with a slip nut. Slide a slip nut and beveled slip washer onto the straight end of the trap arm.
Slide the trap bend up into the tee fitting on the sink drain, while sliding the trap arm into the sanitary tee fitting at the wall.
Adjust as needed to create the most direct path from sink to the wall tee. Make sure trap arm has a slight downward angle toward the wall tee. ?Note: Take care to face the trap the correct way. It may be tempting to turn it the wrong way in order to fit it into a small space, but it doesn’t work properly this way and has a tendency to leak.
Tighten all slip nuts with channel-type pliers. Again, don’t overtighten.
If you have installed a new drain tee in the wall, now is the time to make sure all those joints are secure and permanent.
Run water to check for leaks. Tighten up anything that leaks, and then fill up the sink and give it a good volume test. Do this for both sides of the sink to be sure everything is working properly.