While it may seem like installing a dishwasher is fairly simple, and not much cannot go wrong, this is farthest from the truth. All too often do our home inspectors report on dishwasher drain defects.
We often see dishwasher drains missing a high loop and being installed on the wrong side of the p-trap. Let’s take a look at what this means.
Dishwasher Drain High Loops
What Is It?
The dishwasher drain high loop is a high routing of the drain tube. Having the drain tube go from a low point to high and then back to a low point prevents water backflow into the dishwasher. Therefore, the dishwasher can safely pump its drainage out without water flowing back into the dishwasher.
A Common Defect
This is a quite common defect reported on home inspections. It is very easily overlooked. Also, unprofessional quality is common for appliance installations.
Uniform Plumbing Code
The Uniform Plumbing Code specifically states high loops are required here:
802.1.6 Domestic Dishwashing Machines
“Domestic dishwashing machines shall discharge indirectly through an air gap or air break into a waste receptor in accordance with Section 802.2, or discharge into a wye branch fitting on the tailpiece of the kitchen sink or the dishwasher connection of a food waste disposer. The waste line of a domestic dishwashing machine discharging into a kitchen sink tailpiece or food waste disposer shall connect to a deck-mounted air gap or the waste line shall rise and be securely fastened to the underside of the sink rim or counter.”
Manufactured Dishwasher Drain High Loops
Some dishwasher manufacturers create an additional high loop that is pre-installed on the appliance. This is for additional protection of drainage backflow.
If the appliance manufacturer has a pre-installed drain high loop, this does not substitute for an installer created drain high loop. We know this from the section of the Uniform Plumbing Code above:
“The waste line of a domestic dishwashing machine discharging into a kitchen sink tailpiece or food waste disposer shall connect to a deck-mounted air gap or the waste line shall rise and be securely fastened to the underside of the sink rim or counter.”
What To Do
As a homeowner, you can easily look under your sink or behind the dishwasher to ensure the dishwasher drain loops up before entering the garbage disposal or drain.
If you are missing the dishwasher drain high loop, a simple rerouting process like the image above can help you achieve this. You can also purchase dishwasher drain tubing from Amazon.
More Dishwasher Drain Defects
Missing Dishwasher Drain Clamp
In some cases, we find the clamp missing at the dishwasher drainage tubing. This clamp is needed to fasten the tube to the sink drain securely.
Wrong Side of the Trap
While it is less common in our territory of inspections, home inspectors in states with many older homes often find the drainage tube installed on the wrong side of the sink P-Trap.
The dishwasher drain shall discharge before the sink p-trap like the image above. If your dishwasher drains into piping after the sink P-Trap, sewer gases could get into your dishwasher and home. This may lead to awful smelling dishes and kitchen!
Learn more drainage traps here.
Dishwashers are a common install for homeowners and handymen. As such, home inspectors often find these common defects after an unprofessional install.
Be sure to check your dishwasher at home for a proper high loop, clamp, and to ensure it is draining before the sink P-Trap!
If you have additional questions, comment below!