Dishwasher Drain Line: Common Defects Explained

Smelly Dishwasher? Most Common Problem: The Dishwasher Drain Line.

I think we can all agree that a stinky dishwasher is the worst! As a condominium dweller, I have had this unfortunate experience, sometimes so strong I have prohibited guests into my home. So what is the solution? Often people search for cleaning products for the inside of the dishwasher. However, what about a poorly installed dishwasher drain line?

Remember, a dishwasher connects to your plumbing drainage system. Therefore, there is always a possibility of cross contamination which can lead to health issues. Correct installation of the drain line keeps waste from the sink from backing up into the dishwasher. Thus, installing the drain line properly is critical.

This is the most common problem with dishwashers that I find during my home inspections. Do not worry though, because correcting a dishwasher drain line is easy to solve.

No High Loop Installed

dishwasher-drain-line-high-loop-diagramLook at the diagram above. See how the drain hose loops up to the underside of the counter top? This is a  high loop installation. In Canada, this is the minimum requirement for installations and manufacturers of dishwashers require this configuration too. Try to attach the drain hose directly to the underside of the counter top.

Air Gap Device

An alternative installation to a high loop would be to install an air gap device above the kitchen counter top. Somewhat ugly in my opinion though. In some areas, these devices are becoming mandatory, check with your local building departments for confirmation.


What if there is a garbage disposal under you sink?

If you have a disposal under your sink, do the following:

First, the dishwasher drain line passes through a high loop or air gap. Then slope the drain line down to the connection to the disposal. Finally, the disposal connects to the p-trap and flows out into the drainage stack.

Wrong Connection to Sink Drain

dishwasher drain line

Where the dishwasher drain line attaches to the sink’s drainpipe is also important. Ideally, the connection should be before the p-trap. A p-trap holds water to prevent sewage gases from leaking into the home (in this case the dishwasher too). Therefore, if the dishwasher drain line attaches after, then this could be another source of “stink”.

To summarize

A correct installation of the dishwasher drain line should prevent sewage gases and contaminated water from entering the dishwasher. Which is important for keeping out unpleasant smells, as well as ensuring the everyone’s health. Finally, if you need help to correct your dishwasher drain line, I recommend you hire a reputable licensed plumber.


Thanks for reading, until next time.

Author: Geoff Bohaker for Shelter West Home Inspections

Disclaimer: All information in this blog is provided as a courtesy. Intended for general information only and not intended as legal advice. Reliance upon the accuracy of the information contained herein is at the user’s risk. Shelter West Home Inspections and Geoff Bohaker accepts no liability for any errors or losses that may result from reliance on information contained on this website.




About Geoff Bohaker

Geoff is the owner and operator of Shelter West Home Inspections in Vancouver, B.C., Canada. His boundless curiosity for buildings and how they interact as complete systems, guide him on his journey to educate his clients on making the most informed home decisions possible.
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