Reuben's Home Inspection Blog

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The Most Common Dishwasher Installation Defect

 

An improperly installed drain hose is by far the most common defect that I find with dishwasher installations, but it's also one of the easiest things to get right.  In the photo below, which was featured as a Structure Tech Photo of the Day, there are several plumbing defects, two of which are related to the dishwasher drain.  

Can you spot them?

Dishwasher Drain

Wrong side of trap

Problem number one is that the drain is connected to the sewer side of the trap.  The water that always sits in the bottom of the P-trap is what prevents sewer gases from coming in to the house.  The dishwasher drain must be connected before the P-trap, not after it, which is what was done here.  With this improper installation, sewer gases have the potential to come back in to the dishwasher.  The diagram below right shows a proper installation.

Dishwasher Drain Marked Up Dishwasher Drain Diagram marked up

No high loop

In the diagram above, right, you'll notice that the dishwasher drain makes a high loop underneath the kitchen sink.  This is the minimum requirement on every dishwasher drain installation - it's required by every manufacturer of dishwasher, and it's also required by the Minnesota State Plumbing Code (section 4715.1250).  In fact, our plumbing code says "as high as possible under the countertop."  An alternative to installing a high loop is to install an air gap at the kitchen sink, but I can't imagine why you would do this if you didn't have to - how ugly.  I've heard that these air gaps are required in California.  Too bad for them.

Dishwasher Drain Loop Photo Dishwasher Drain Loop Diagram

Although new dishwashers come from the manufacturer with the drain looped up at the side of the dishwasher, every installation manual still requires this high loop underneath the sink.

Dishwasher Integral Drain Loop

I've heard different reasons for why an additional loop is required under the sink, so I decided to contact the manufacturers directly.

I sent out an email to eight dishwasher manufacturers, asking them this question:

"In the installation instructions for all of your dishwashers, a high loop is required on the dishwasher drain. What is the purpose of this? Doesn’t the high loop that is incorporated in to the side of the dishwasher achieve the same thing? Any insight or commentary in to this matter would be greatly appreciated."

Here are the responses I received:

  • Kenmore: "The high loop or air gap must be used to prevent potential backflowcontamination of the dishwasher. Local plumbing codes generally dictate the requirements in your area. Section 807.4 of the Uniform Plumbing Code states: "No domestic dishwashing machine shall be directly connected to a drainage system or food waste disposer without the use of an approved dishwasher airgap fitting on the discharge side of the dishwashing machine. Listed airgaps shall be installed with the flood level (FL) marking at or above the flood level of the sink or drainboard, whichever is higher, or separately trapped with the airbreak located on the stand pipe."
  • GE: "If an air gap is not required, the drain hose must have the high loop from the floor toprevent backflow of water into the dishwasher or water siphoning out during operation."
  • Bosch: The high loop in the drain hose of your dishwasher is to keep water from settling in the hose if it were hanging down any lower or horizontally. This keeps the drain hose dried out and keeps any odors from backing up into the dishwasher.
  • Viking: In testing our dishwashers, we have found that the additional high loop in the back of the dishwasher is required for proper draining of the water.  We have seen when this piece is not applied that over time the consumer will have issues with the water back up and causing issues with proper drainage and water pooling in a particular area.
  • Maytag: No response after 29 days.  Boo.
  • Whirlpool: No response after 29 days.  Boo.
  • Amana: No response after 29 days.  Boo.

To summarize, the reasons for the high loop are to prevent potential backflow of water in to the dishwasher and to prevent improper drainage of water.  Even though dishwashers come from the factory with the drain looped up high against the side of the dishwasher, this is not an acceptable substitute for the high loop underneath the kitchen sink.In Minneapolis, the lack of a properly installed high loop under the kitchen sink requires repair for their Truth-In-Sale of Housing evaluations.

 

Reuben Saltzman, Structure Tech Home Inspections

        

Comment balloon 27 commentsReuben Saltzman • July 20 2010 06:39AM

Comments

It is a scary picture. It is important to hire  a registered plumber to install a dishwasher.

Posted by Gita Bantwal, REALTOR,ABR,CRS,SRES,GRI - Bucks County & Philadel (RE/MAX Centre Realtors) about 8 years ago

It is almost on every house we see....why can't they teach the correct installation to the appliance installers?  It is not that complicated.

Posted by Yvette Chisholm, Associate Broker - Rockville, MD 301-758-9500 (Long & Foster Real Estate, Inc.) about 8 years ago

Good information, Reuben. It always best to do it right the first time.

Posted by William True, Sarasota Real Estate (True Sarasota Real Estate) about 8 years ago

Gita - and if your plumber doesn't like reading installation instructions, this is what you might get. 

Yvette - no, it's really quite simple.  It takes about 30 seconds to get this right the first time.

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) about 8 years ago

William - a long time ago, when I used to think that the integral loop was an acceptable substitue, I installed my dishwasher without the extra loop under the sink.  About a year later, the drain ended up getting completely blocked up with 'crap'.  

I replaced the drain hose and installed it the way it should have been done the 'first time', and it's worked fine for the last six years.

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) about 8 years ago

The problem I used to have with the dishwasher installation (doing rehabs) was that it wouldn't drain, only to find that I forgot to remove the plug from the new disposal. It only takes once to never forget that again.

Posted by Bill Travis, Broker/Owner (Captain Bill Realty, LLC) about 8 years ago

Reuben, here we are required to have an air gap device (counter-top or Johnson-T usually).  Some jurisdictions allow the one built into newer washers but the city of Seattle requires a separate one.

Posted by Charles Buell, Seattle Home Inspector (Charles Buell Inspections Inc.) about 8 years ago

Bill - I can imagine.  What a quick fix, but what a mess!

Charles - I'm so sorry to hear that.  Crawl spaces, air gaps... why live there?  Oh yeah, the weather.

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) about 8 years ago

Gee, thanks.  I've had drainage issues ever since my own new dishwasher was installed, and I could swear there's no high loop there.  Really eager to get home now!

Posted by Catarina Bannier, DC Real Estate The Smart And Fun Way (Compass) about 8 years ago

Catarina - let me know what you find.

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) about 8 years ago

Looks like the drain goes uphill as well where the dishwasher tailpiece is installed.   Good, infomative post and thanks for sharing.  I've actually had a few plumbers in our area question me on this.

 

Posted by Joshua Frederick, Home Inspector in Defiance & all of Northwest Ohio (Home Inspector for ASPEC Residential Services, LLC) about 8 years ago

Joshua - you're correct, that drain is supposed to go down, not up.  If you ever have plumbers question you, it's very easy to find the installation instructions online, and they trump everything.

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) about 8 years ago

Thanks, Reuben.  Here we go:  the flexible drain pipe comes up from the bottom (dishwasher is on the right; no clue if there's a loop inside as that's obscured), loops a bit on the ground, then goes straight up to some connection with the garbage disposal, not directly into the trap.  Or is that the "air gap" you were talking about?  We've had tiny food particles stuck to our glasses (almost burned in by the drying process) ever since this dishwasher was installed a couple of years ago.  An LG repair partner/contractor type came recently and told us there was nothing that could be done as all the newer, "higher efficiency" dishwashers just didn't use enough water to get the job done properly.  This makes no sense to me--especially since we now have to prewash everything we put in there!

Posted by Catarina Bannier, DC Real Estate The Smart And Fun Way (Compass) about 8 years ago

Hi Reuben, a great refresher on the proper way to pipe the dishwasher drain.  Thanks

Posted by Dale Ganfield about 8 years ago

Catarina - thanks for the photos, that helps.  Your drain installation is proper - yes, that's an 'air gap'.  I'm sorry your dishwasher doesn't wash your dishes!  

I don't believe your repair person's excuse.  According to Consumer Reports, modern dishwashers do such a good of cleaning dishes that there is no need to pre-rinse / pre-wash your dishes.  I think your dishwasher has a problem.

Dale - thanks for reading.

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) about 8 years ago

Reuben--thanks so much for "inspecting" my pipe!!  I'm relieved to hear it's installed properly, but also disappointed that i haven't found the quick fix i was getting excited about ;-) 

At least I can leisurely throw the term "air gap" around at the next home inspection!  ("Oh, Paul, doesn't that air gap look hideous the way it pokes out of the pretty sink there?")

Posted by Catarina Bannier, DC Real Estate The Smart And Fun Way (Compass) about 8 years ago

Reuben

Have you ever had the plumber argue that the high loop is not required?  We have run into that a couple of times.

Richard Acree

HABITEC Home and Building Inspections, LLC

http://habitecinspections.com

Posted by Robert Dirienzo, Home Inspections - Nashville TN (HABITEC Home and Building Inspections, LLC) about 8 years ago

Catarina - my pleasure.  Let me know what the outcome is :)

Richard - never.  You've seriously had plumbers tell you that the manufacturers installations instructions don't need to be followed?  That's just silly.  It would probably take less time to fix this than to argue about it.

Thankfully, we have this requirement specifically spelled out in our state plumbing code, so there's really no way to argue about this one here in MN.

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) about 8 years ago

Great information I did not know.  Thank you,

Aaron

Posted by Aaron Silverman, Improving Real Estate Experience through Education (SuccessfulRental.com, Bluewater Property Management, LLC and Lowcountry Turnkey Properties, LLC) about 8 years ago

Very useful information. We get several calls a year for sewer odors coming from the dishwasher. Most of them were not installed by a plumber.

Posted by Local Charleston Plumber (Rooter Man Plumbing and Drain Service) about 8 years ago

another error is the electrical outlet under all those water pipes. as bad as it looks its very common to see things like that. there are plenty of sloppy people out there.

Posted by george almost 7 years ago

another error is the electrical outlet under all those water pipes. as bad as it looks its very common to see things like that. there are plenty of sloppy people out there.

Posted by george almost 7 years ago

another error is the electrical outlet under all those water pipes. as bad as it looks its very common to see things like that. there are plenty of sloppy people out there.

Posted by george almost 7 years ago

We just bought a new Bosch dishwasher & the drain hose end that goes into the garbage disposal is too small. 3/4"

The old dishwasher hose was 1" at the disposal end.  What can we do?

Posted by Marie about 6 years ago

http://fixitnow.com/wp/2010/02/08/dishwasher-drain-hose-adaptor-a-haiku-of-praise/

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) about 6 years ago

I just tried installing my new Samsung Dishwasher and all was well except the drain hose is too short.
I thought maybe I'd use my old one, but it looked like my old one wouldn't attach and seal as nicely to the new dishwasher like this one was, plus the boot is soo large on my old hose and there is practically no room to get your hands in there to take the old one out.  is there a simple extension I could buy.  I searched online but didn't see any.  I thought maybe I could go to lowes or some hardware store tomorrow.   Any Ideas?

Posted by Rick almost 6 years ago

Hi Rick,

I think your best option would be to contact Samsung.  Some manufacturers don't want the drain line extended.

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) almost 6 years ago

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