How to Connect a New Dishwasher to an Existing Drain
- 1). Locate the straight drain pipe that connects the bottom of the sink drain to the curved pipe, called a P-trap. There is a large nut on either end of the straight pipe that fastens it in place.
- 2). Unscrew the nut at each end of the straight drain pipe using a pair of slip-joint pliers. Gently remove the pipe from between the drain stub and the P-trap.
- 3). Cut the new length of straight pipe with a side port using a hacksaw; use the old pipe as a guide.
- 4). Install a plumbing nut on each end of the new straight pipe with the threads pointing toward the ends. Install a gasket in front of each nut with the flanged part of the gasket pointing toward the ends of the pipe.
- 5). Fit the pipe between the drain stub and the P-trap and thread the nuts on each end. Hand-tighten the nuts, then turn them 1/4 turn using the slip-joint pliers.
- 6). Insert the dishwasher's drain hose onto the side port of the pipe you installed. Tighten the clamp around the end of the drain hose using a screwdriver to turn the screw clockwise.
Source...