You do not need to hire a professional plumber to install drain pipes underneath your sinks. No matter what the configuration is in your kitchen or bathroom, you can install the correct drainage yourself. In fact, it's a great project to start with if you're looking to develop some basic plumbing skills.
Step 1 - Configuration
Inspect underneath your sink to determine which shapes of pipe you need. You will need a piece of pipe to connect your sink drain either directly to the wall trap or to the garbage disposal before running pipe to the wall trap. You may also need to construct the shape of your plastic drain pipe so that will work for your sink configuration. This can be done by fitting pipes together with plastic nuts and washers.
If you need to connect a disposal with your drain pipes, you'll need a "T Junction." You might also need to use an "S Trap" to connect them to the wall.
Step 2 - Pipe to Sink Strainer
The first thing you need to do when you install drain pipes is secure your sink basket strainer in the sink. The bottom of the strainer has a small piece of pipe sticking down which you can connect to your drain pipe. Make sure you use the metal washer that comes with the basket strainer. You need to make sure the basket strainer is securely fitted in the sink and does not move around. Put some putty on the underneath of the sink strainer and press it into the sink drain to secure it into place.
Next, take the piece of PVC pipe that will attach to the sink basket and fit it along with a plastic washer using your adhesive. Apply more adhesive to the end of the pipe and slide on the metal nut to secure the plastic pipe to the sink basket before tightening it with a wrench.
Step 3 - Sink Pipe to Disposal (Only If Needed)
If you have a garbage disposal, you must connect it to the rest of your drain pipe so that anything that runs into the sink or disposal also runs through the drain pipe, into the wall trap and out of the system.
Put a plastic nut and washer on the disposal elbow (the piece of pipe coming out of the side of the disposal), apply some adhesive to the PVC pipe and screw it onto the disposal elbow. The pipe you attach to the disposal will have to be a T-shaped piece with a raised end outlet. Part of this pipe will be hanging down once fitted, and this can be connected to the wall to stop it moving.
Step 4 - Disposal to Wall
Place two plastic nuts on the wall trap (the metal pipe sticking out of the wall where everything flows out of the house) with one facing the wall and one facing the opposite way. You will need to use your S-shaped piece of pipe and attach it to the piece of pipe that is still open (in this case coming off of the garbage disposal). Attach it like the other pieces of pipe using nuts, washers and adhesive.