One of the most common dishwasher faults I find as a home inspector in the Houston area are improper drain installation.
In most Harris county homes, the dishwasher is connected to the food disposal for drainage of waste water. Because there is a direct connection between the food disposer and the dishwasher we must prevent back flow into the dishwasher from the disposal.
Imagine your clean dishes in the dishwasher being exposed to waste from the disposal. The potential for harmful bacteria is significant so we want to do all we can to ensure back flow does not occur.
There are two methods approved by the building codes to accomplish this.
The simpler of the two is the “high loop” method.This method simply involves attaching the drain hose as high as possible under the counter.
Ideally, it should be attached to the bottom of the counter or counter substrate (usually plywood). If this isn’t possible, attach it as high as possible on the cabinet.
The high loop prevents back flow from the disposal by gravity. Any waste from the disposal has to travel uphill before it can get to the dish washer. High loops are not the ideal solution, as the disposal can act as a pump and physically push the waste into the dishwasher.
Your other choice is an air gap and it is a much more effective device for preventing dish washer contamination.
©2018 Patrick Miceli