Accessing the Tube
A clogged tube is usually due to large debris or algae growing inside the tube. To clear it out, you need to access it. The drain tube is usually located behind the back panel in the freezer or in the refrigerator unit itself. Remove the back panel of the freezer by pulling out the plastic plug along the perimeter of the panel and removing the screws. The drain tube is located at the bottom. Inside the fridge, the drain tube will be on the back wall in plain sight.
Clearing the Tube
There are two ways to clear out the tube -- with another plastic tube or a copper wire. Stick the wire down the drain tube to break up any clogs. You will likely feel a small amount of resistance but don't force the wire; this may cause damage to the tube. Alternatively, place a plastic tube inside the drain tube and blow into it to break up the clog.
To prevent future problems, it is best to kill any algae that may be living in the drain tube. Suck up a small portion of diluted bleach into a turkey baster. Squirt the bleach into the drain tube to kill the algae. Unplug the unit from the socket and pull the fridge out from the wall. Locate the drain pan by the motor. Lift it out gently and clean it with a diluted bleach solution as well.
Not all leaks are due to a clogged drain tube. The most common leak issue is due to a badly balanced fridge. A fridge needs to tilt back slightly so that water will travel towards the drain tube. Stack three quarters on the top of the fridge and place one end of a spirit level on top of the quarters. The bubble should indicate the fridge is level from front to back. If not, adjust the legs of the fridge according to the instructions in your owner's manual.