Dishwasher Air Gap/High Loop

One of the most common kitchen defects I find is an incorrect installation of the dishwasher drain connection. Often times homeowners purchase and install their dishwasher and are unaware of certain requirements. Air gaps may also be difficult to install if the counter or sink is not set up for the penetration through the sink/counter. Lets discuss the current requirements and reasons for them.

Dishwasher drains are commonly connected to the local sink drain. This can lead to cross contamination if the sink drain backs up and may divert dirty water into the dishwasher. To prevent this a “High Loop” or “Air Gap” is required. A high loop is formed by routing the drain hose up to the underside of the counter top before running the drain hose back down to the disposal or sink drain. This helps prevent the possibility of cross contamination. This type of drain is no longer allowed in Wisconsin, an Air Gap is currently required. So for the purposes of this post I will concentrate on Air Gaps.

Residential dishwasher drains must:

  • Discharge to the plumbing waste system
  • Not exceed 10 feet in length
  • Incorporate and Air Gap or separate stand pipe drain

Air Gap Installation Above Counter

A dishwasher air gap is a plumbing fitting that extends above the counter and incorporates a “Y” pipe to force the water above the edge of the sink to prevent sink water from making it’s way into the dishwasher. Air gaps can be installed above the counter or below, but certain rules apply. When the air gap is located above the counter the drain can be connected to the local sink drain or garbage disposal. The drain hose from the air gap to the disposal cannot exceed 18 inches in length.

Air Gap Below Counter

When the air gap is located below the counter the drain must discharge into a separate stand pipe that meets the following requirements:

  • Measures a minimum of 1 1/2 inches in diameter
  • Measures minimum of 15 inches in height above the trap weir

These requirements listed in this post were taken directly from the Wisconsin administrative code: SPS 382.33(9)(d). They are the most current standard as of this writing. At the time of your dishwasher installation these requirements may not have been in place, but upgrading your drain to meet these standards would be a wise idea to prevent issues down the road. Also, the parts required to bring your drain into compliance are inexpensive. As always, if you don’t feel comfortable with the task at hand, a consultation with a qualified, licensed plumber is recommended.

As always, I hope you have taken some value from this post. If you have a suggestion for a maintenance topic please submit them to my email below.



Aaron M. Zuehlke is the owner and inspector at Zuehlke Inspection Service, LLC, a full-service home inspection company serving Southern Wisconsin. Specializing in Home inspection, Radon Testing, Mold Testing/inspection, Residential Thermal Imaging, and Manufactured Home Foundation Certifications. He also manages several rental properties through Zuehlke Properties, LLC. He can be reached by email at or by calling the office at 608-931-7485.

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