A dish drawer is a dishwashing unit comprised of two separate washers stacked one on top of the other. It occupies the same space a regular dishwasher does and holds the same load when both drawers are used. It makes washing a small load more energy efficient, as only one washer runs. In addition, one drawer can be set on gentle for crystal and china, while the other is set to clean heavy pots and pans.
The dish drawer offers flexibility. They don't have to be stacked on top of each other. Put one drawer near a prep station and one near plate storage. Tall people load and unload a high-mounted dish drawer without having to bend over, while wheelchair users appreciate the simple pullout design that keeps everything within easy reach. A single dish drawer makes a wet bar amenity.
Each drawer occupies about 17 inches of height, making under-the-sink installation impossible, even for one drawer. The trap is in the way. Even if squeezed in, there would be no room to work on sink plumbing without removing the dishwasher.
If you lack kitchen space, use the dishwasher's two-part design putting each drawer in a convenient place. Purchase a single drawer if that's all you need. A regular dishwasher needs much floor space, so that its door folds down, while an open dish drawer requires less clearance. If you need a taller or wider dish drawer, some manufacturers now offer them.