Reinstall the filter, upper screen, and dishwasher rack. Occasionally, debris can make it past the dishwasher filter, potentially leading to a clogged dishwasher drain hose. This is even more likely ...

Drain hose: Finally, connect the drain hose to your dishwasher if it wasn't already. Feed the attached drain hose from the dishwasher through the hole in your cabinet.

Otherwise, you can access the drain hose by removing the kick plate on the front of the dishwasher. Check the accessible bits of the hose (probably under your sink).

As you slide the old dishwasher out, you'll have to simultaneously work the drain hose back through the hole in the sink cabinet. Keep a rag handy to wipe up the water that will run out of the line.

The dishwasher drain must be connected before the P-trap, not after it, which is what was done here. With this improper installation, sewer gases have the potential to come back in to the dishwasher.

In either case, the hose you buy must be heat- and detergent- resistant. You can find ready-made dishwasher drain hoses, but 5-8th-inch automotive heater hose is a common alternative.