A dishwasher's drain line connects to the kitchen sink's drain system, either by the drainpipe or the garbage disposal if one is installed. Waste water from the sink's drain that flows into the dishwasher creates a potential health hazard, making finding the cause of the problem something you should not put off.
Dishwasher drain lines may have an air gap piece in the line, which looks like a metallic cylinder that is mounted on the bottom of the sink near the faucet. The air gap creates a section of air in the dishwasher's drain line, which should keep dirty water in the sink's drain line from flowing back into the dishwasher, even if the sink's drainpipe has a clog that keeps the dishwasher's waste water from emptying.
Clogs may create extra pressure in the sink's pipes, forcing the water to flow up the dishwasher's drain line and into the dishwasher. You may relieve the pressure in the pipes and remove the clog by taking apart the pipes, but you must have a bucket under the pipes to catch the trapped water. If you do not find the clog in the pipes, feed a drain snake down the pipe in the wall.
If you choose to plunge your clogged sink's drain line, you must take precautions to avoid having the waste water in the sink's drainpipe flow into the dishwasher's drain line and enter the dishwasher. A plunger applies pressure to drainpipes, enough pressure to overcome the dishwasher drain line's air gap. To keep this from happening, you must clamp the dishwasher drain line where it meets the sink's drainpipes or the garbage disposal.
Dishwasher Line Clog
When no clogs in the sink's drainpipes exist, the problem of dirty water flowing into your dishwasher may be with the dishwasher's drain line. Food debris that washes off dishes and makes it through the strainer that surrounds the dishwasher's pump flows into the dishwasher's drain line. Eventually these small pieces of debris clump together and clog the drain line, meaning the waste water flows out of the dishwasher, but then it contacts the clog and flows back into the dishwasher. To flush out clogs in the line, you must loosen the clamps on both ends of the drain line using a screwdriver, and then hold the line up to a strong stream of water.