Dishwasher High Drain Loop And Air Gap (Anti Siphon)

What is the difference between a dishwasher high loop and an air gap (anti siphon)? Which one is a better method to prevent water entering the bottom of dishwasher?

Dishwasher air gap - high drain loopDishwasher – air gap – high drain loop

The purpose of a dishwasher high drain loop is to prevent back flow of water. The water can flow back into the dishwasher which will leave water in the bottom of the dishwasher. The high drain loop is also there to prevent improper drainage of water while the dishwasher is running. The high loop does not prevent siphoning.

High drain loop - DishwasherHigh drain loop – Dishwasher

VIDEO – Dishwasher High Drain Loop

The purpose of a dishwasher air gap or anti-siphon is to prevent the siphoning and back flow of water. The water can flow back into the dishwasher which will leave water in the bottom of the dishwasher. The air gap or anti siphon prevents siphoning if sinks are drained simultaneously.

Air gap - DishwasherAir gap (anti siphon) – Dishwasher

VIDEO – Dishwasher Air Gap

  • Both the HIGH LOOP and AIR GAP methods prevent the drain water from your sink from routing into the bottom of your dishwasher when you drain your kitchen sink.
  • The anti-siphon method is best as the air gap makes it unlikely for dirty water and bacteria to reach the dishwasher.
  • The high loop method may become an issue if both of your kitchen sinks are drained at the same moment. If the kitchen sink was clogged partially, the draining water may reroute into the bottom of your dishwasher. If water gets into the bottom of your dishwasher then when you start the dishwasher for its initial wash cycle, the waste water is combined with the clean water and may not clean your dishes completely.
  • When the dishwasher is in its drain cycle, you will hear a gurgling noise coming from the kitchen sink drain. If any water or waste is backing up the line, there is some issue with the drain itself.
  • Installing a high loop is very easy compared to an anti-siphon (air gap) device will involve drilling the kitchen sink or counter top so you can install the anti-siphon. Some kitchen sinks have a hole already and this hole may be used for the anti-siphon or air gap device.

dishwasher drain hoseDrain Hose – Dishwasher


dishwasher air gapAir Gap – Dishwasher

ALLEN VETTER - DIY Repair Assistant
Allen is a Home Maintenance/Appliance Tech and the author/creator of this website. He has 33 years of experience troubleshooting and repairing all types of appliances. Contact here

1 thought on “Dishwasher High Drain Loop And Air Gap (Anti Siphon)”

  1. Henry Chinery

    I had my kitchen flooded when the disposal got clogged by the tenants who then ran the dishwasher. As the dishwasher cycled through it filled the sink to overflowing so they turned the dishwasher off. The water promptly siphoned back into the dishwasher through the high loop and out onto the kitchen floor. So it’s air gaps for me, preferably metal ones.

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