A portable dishwasher usually has wheels on the bottom, and it doesn't require the support of cabinetry to keep it upright. A common problem with these dishwashers is that water doesn't completely drain from the tub. A small amount of water usually stays in the tub to keep the water seal lubricated. If you see any more than between 1 and 3 cups, troubleshoot and repair the problem to save money.
All portable dishwashers have a pump that pushes water out of the tub and into the drain. If the pump is clogged with food particles or debris, it won't work properly. Unplug the dishwasher from the power source, and remove the spray arm, spray arm support and bottom rack. Clean out the pump and nearby filters. Examine the pump, and see if any parts are broken. The impeller looks like a fan, and it is the most common part of the pump to break. You must replace the whole pump if any part on it is cracked or extremely worn. You usually can't repair the pump.
Air Gap/Drainage Hose
The air gap has a cap over it, and it is usually near the sink. Lift up the cap, and dig out any debris inside the air gap. The drainage hose captures water moving out of the tub and takes it to the household drain. Use a plastic spoon to clean out the drainage hose if it's dirty. See if the hose is kinked, and straighten it. If the hose is crushed or badly kinked, you need a new one. Attach the drainage hose beneath the countertop if you don't have an air gap. This creates a high drain loop, which prevents water from the sink from entering the portable dishwasher tub.
Household Plumbing/Drain Valve
The drainage hose must connect to either the air gap or the household drain. If the home drain is clogged, the dishwasher won't drain. Clean out the drain and internal plumbing with plumbing supplies. The drain valve is located inside the drainage hose. It has a solenoid that causes it to open and close. Use a multimeter, and test this solenoid for resistance. If you don't get a reading between infinity and 40 ohms, the solenoid is defective, and you need a new one. Remove any objects stuck in the valve.
If you haven't used your portable dishwasher for a while, the motor can get stuck. Unplug the dishwasher, and remove the main access panel. Turn the motor to free it. If the motor is still stuck or is burned out, get a new one from a dishwasher parts dealer. The timer regulates which component gets power and for how long. Use a multimeter, and see if the timer has continuity. If not, replace it since it's difficult to repair the timer.