Final answer:
The dishwasher drain line should be connected to the sink's drain plumbing before the P-trap to prevent backflow and ensure proper drainage. A high loop is often included to further prevent the possibility of contaminated water siphoning back into the dishwasher.
Step-by-step explanation:
The dishwasher drain line must be installed correctly to ensure that wastewater is properly expelled from the dishwasher and to prevent any contaminated water from flowing back into the dishwasher. The drain line should be connected in reference to the trap under a kitchen sink.
Typically, the drain hose is attached to the sink's drain plumbing either by connecting to a garbage disposal unit with a drain port or directly to the sink drainpipe before the P-trap, which is a curved section of pipe that retains water to prevent sewer gasses from entering the home. It's important not to connect the drain hose directly to the sewer line without going through the P-trap to avoid potential health hazards and to comply with plumbing codes.
Moreover, to prevent dirty water from the sink from siphoning back into the dishwasher, it is common practice to install the drain line with a high loop. This means the hose is looped at a height typically higher than the bottom of the sink before it goes down to the drain connection. This high loop acts as an additional safeguard against backflow.