Do I Need a P-Trap on My Garbage Disposal Drain?

Garbage disposals help to break down food and other materials left over after a meal. They are installed beneath kitchen sinks and held in place by special metal collars. Once the material inside is broken down, it is then washed out into the sewer system connected to the disposal. P-traps are curved sections of pipe connected between sink drains and the sewer pipe inlet.

Garbage Disposal Basics

Garbage disposals are designed to break food before passing it down into the sewer system. This helps prevent pipes from getting clogged with food debris and other materials. Disposals use a series of blades inside the disposal chamber for cutting up the food materials. They are powered by electricity, either from a nearby plug or wired directly into the wiring system. Dishwashers can be connected to a disposal at the side.


A p-trap is a curved piece of pipe designed to prevent sewer gases from escaping upwards. The bend in the bottom of the pipe keeps water trapped inside. When gases start to seep up through the pipes, they are blocked by the water in the bottom of the p-trap. P-trap requirements and regulations are usually set out in local plumbing codes and ordinances. They are used on just about every plumbing fixture, including sinks, bathtubs and (in a somewhat modified form) on toilets.

Garbage Disposal Plumbing

The outlet on a garbage disposal is the same as kitchen pipe plumbing, typically 1 1/4 inches. This allows the disposal to be connected to the existing plumbing. Rerouting the existing plumbing is usually required when a new garbage disposal is installed. The tailpiece beneath the drain is removed to make way for the disposal, and the outlet on the disposal connected to a sewer pipe inlet. The plumbing connections are usually compression type mounts on most garbage disposals.

P-traps and Garbage Disposals

In most municipalities, p-traps are required on garbage disposals. Even though the disposal may seem substantial in size, it cannot block gases leaking up through the pipes below. Check the local plumbing codes in your area (usually available at your City Hall or records office) to see what the local laws require.