The outlet of the disposer is called a “tail pipe”. The plastic tail pipe connects the disposer to the sink trap that empties into the drain system. A new plastic tail pipe comes with each disposer. It is cut or extended to connect with the trap.
Exploded View of a Disposer
A sink trap is necessary to minimize odors. Water sitting in the trap blocks out sewer gases coming from the drainage system. In the past, sink traps were made of light gauge chrome-plated brass. They rust out and leak after 15-20 years. It’s wise to carry a universal trap in your truck. Sometimes old traps will crack just by removing it from the sink. Modern traps are made of PVC plastic and are much more durable.