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The Ancient and Mystical Art of Dishwasher Drainology
Your dishwasher sounds like it's working up a storm, draining all that yucky dirty water out, but you open the door and all that dirty water is still there. Houston, we have a problem. Ok, grasshopper, go grab you a cold one and hang on for a magical mystery tour into what causes dishwasher draining problems, also called the ancient and mystical art of dishwasher drainology. Let's take 'em one at a time:
Using Too Much Detergent
Some fancy dishwashers with electronic controls have sensors that detect when the pump is not pumping water. Using too much detergent creates a great head of foam in the dishwasher basin, like pouring a beer too fast into a glass. So if you use too much soap in one of these so-equipped dishwashers, the sensors think the dishwasher is empty and cuts off the pump (For you gadget geeks out there, it senses the pump work by using a sensing resistor in series with the motor main winding.) While we're talking about detergents, that store bought stuff you're using is screwing up your dishwasher.
You Forgot to Remove the Disposal Drain Port Knockout Plug This usually only applies to the situation where you just installed a disposal and connected the dishwasher drain hose to the drain port on the disposal. Believe it or not, this happened to me on my first disposal installation job, too...no, not really. But I have seen many a grasshopper stumped by this.
Drain Solenoid Not Opening
Some brands, notably GE/Hotpoint and Magic Chef, use a drain solenoid to open and close the dishwasher drain port. If this solenoid isn't opening during the drain cycle, could be a bad timer or solenoid.
Worn Pump Impeller
Other dishwashers, like Whirlpool and KitchenAid, don't use a drain solenoid but instead reverse the motor to drain the basin. One possible reason for poor draining in this type of dishwasher is a worn pump impeller. You usually figure this by elimination...no, not that kind of elimination you dawg! I mean, if all the other suspects listed here check out ok, then you've got a worn pump impeller. The rebuilding kit for this repair is very inexpensive and is a great beer drinking project.
Kinked or Plugged Drain Hose
Drain hoses can become kinked or crimped from poor installation, stuff being moved around, lots of reasons. It happens. This page on drain hose configurations shows you several approved drain hose layouts. Drain hoses can also get plugged from gookus. Plugs usually occur at the one of the drain ports--either on the dishwasher or at the other end. The best test is to take the drain hose off at the dishwasher and pucker up and blow like a fish. Yep, it can be pretty nasty putting your mouth on that stuff but, hey, that's why we appliance techs make the big money.
Air Gap Plugged with Gookus Plumbing codes require an air gap in your dishwasher drain hose and many houses have 'em. These air gaps do a great job of keeping sewer water from backing up into your dishwasher but they can become a source of problems, too. Sometimes, they'll get plugged with gookus and they'll need to be cleaned out. If it's real bad or corroded, do yourself a favor and install a new air gap kit.
Your dishwasher sounds like it's working up a storm, draining all that yucky dirty water out, but you open the door and all that dirty water is still there. Houston, we have a problem. Ok, grasshopper, go grab you a cold one and hang on for a magical mystery tour into what causes dishwasher draining problems, also called the ancient and mystical art of dishwasher drainology. Let's take 'em one at a time:
This usually only applies to the situation where you just installed a disposal and connected the dishwasher drain hose to the drain port on the disposal. Believe it or not, this happened to me on my first disposal installation job, too...no, not really. But I have seen many a grasshopper stumped by this. 
Plumbing codes require an air gap in your dishwasher drain hose and many houses have 'em. These air gaps do a great job of keeping sewer water from backing up into your dishwasher but they can become a source of problems, too. Sometimes, they'll get plugged with gookus and they'll need to be cleaned out. If it's real bad or corroded, do yourself a favor and install a new air gap kit.
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