Virtually every hardware store will have a vast array of PVC drain pipes to fit your plumbing project. A garbage disposal has two possible connecting points: the main drain pipe and the dishwasher drain pipe. The main drain pipe will always be connected, but depending on your needs, the dishwasher drain pipe may or may not be needed.
Main Drain Pipe
Each garbage disposal comes with a PVC tail piece. Because most garbage disposals are attached directly to the j-bend, the tail piece will have an immediate 90-degree bend as it comes off the disposal. If you need a longer tail piece pipe run or the drain lines are in an awkward position, however, an extension can be attached for length, or a flexible tail piece can be attached that will bend and conform to drain pipes that are in awkward positions. All PVC tail pieces, regardless of how they are used, attach to the disposal by first inserting a rubber gasket between the tail piece and the disposal, then securing the tail piece with two bolts that thread into the side of the garbage disposal unit.
If you have a dishwasher, it will need to be drained. Every garbage disposal contains a short thin drain pipe near the top of the unit. Before you attach the dishwasher drain line, the tab in the dish washer drain pipe on the disposal unit must be punched out. The PVC drain pipe from the dishwasher will have a rubber gasket at the end of the pipe. Push the gasket over the dishwasher drain pipe on the garbage disposal and tighten the hose clamp on the end of the pipe. This step is optional. If you scrape the dishes and remove the food particles from them before you insert them into the dishwasher, you can attach the dishwasher drain pipe directly to the sink drain by inserting a specialty dishwasher drain pipe directly above the j-bend pipe.
Flex Pipe Extension
For awkward or offset drain pipe connections, connect a PVC flex pipe to the main drain line. A small tail piece must be inserted first and bolted into place. The PVC flex pipe is pushed onto the tail piece and tightened on using a plastic compression gasket and a hand-tightening PVC pipe nut. The flex pipe is then bent into the correct position so that it attaches to the main PVC drain pipes.
Double Sink Connections
A double sink connection will require the use of a long tail piece extension and possibly a regular PVC pipe extension to join the sinks together. The extension is attached to the tail piece using a plastic compression gasket and a hand-tightening PVC pipe nut. In most cases, the garbage disposal gets attached to the side of the double sink that is farthest from the main drain. A PVC tee outlet joins the plumbing from both sinks together and sends the waste water down into the j-bend.