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What is a Dishwasher high loop?

A high loop in a dishwasher installation is a method used to prevent backflow of dirty water into the dishwasher. It's a crucial step in the installation process, ensuring the proper functioning of the appliance and maintaining hygiene. Your high loop on the dishwasher should look like an upside down P trap.  And it’s a very common defect found during the home inspection. It can also easily be fixed and wont break the piggy bank..


The high loop prevents wastewater from siphoning back into the dishwasher from the sink or garbage disposal. This helps avoid contamination and keeps the dishwasher clean.

Do I need a high loop:

Yes, you do… end of story. It is required by plumbing code, and is also a good idea for you to not have wastewater siphoning in your dishwasher.

Additional Tips:

  • Proper Positioning: Ensure the loop is high enough to prevent backflow. The loop should be as high as the countertop.

  • Check Local Codes: Some areas may have specific plumbing codes that dictate the installation height and method.

  • Air Gap Installation: In some regions, an air gap may be required by code instead of or in addition to the high loop. An air gap provides a visible gap to prevent backflow and is installed on the sink or countertop. MN does not require an air gap anymore.

  • High loop on dishwasher: most dishwashers already have a high loop on the side of the dishwasher or built in it, but you still need to have a high loop before the plumbing enters the waste line.

Pic below= no high loop.

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