Q: A client wants to locate her dishwasher in a peninsula several cabinets away from the kitchen sink. Are there any limitations on the distance that the discharge hose can travel, or should it be plumbed separately?
A. Mike Casey, a licensed plumbing contractor and co-author of Code Check Plumbing, responds: Most dishwashers come from the factory with a 6-foot 6-inch drain hose, and nearly all manufacturers allow this hose to be extended to a maximum total length of between 10 and 12 feet. A heat- and detergent-resistant 7/8-inch inside-diameter extension hose can be connected to the existing hose with a section of 3/4-inch inside-diameter copper tube. During installation, try to keep the number of bends low and the run as short as possible, since a lot of bends and a long run will increase the load on the dishwasher waste pump.
Dishwasher hoses should have a high loop at least 20 inches above the finished floor to prevent wastewater from entering the appliance if the drain clogs. Code requires that the hose connect to the sink drain on the sink side of the trap, typically with a branch tailpiece.
Some jurisdictions require an air-gap device, in which case the hose should connect to this device first, then terminate at the branch tailpiece or garbage disposal.