This is nutz. Stormin Mormon's got it right, but no one's listening to him.
Welcome to Fridges 101:
In the freezer compartment of your fridge, you will find a removable panel.
Behind that panel will be the evaporator, the defrost heater, the defrost thermostat and the evaporator fan. The evaporator is a coil of aluminum tubing with fins all over it. It's the source of "cold" in your fridge. The evaporator fan draws air through the evaporator and blows that cold air into the freezer compartment (mostly) and also some goes in at the bottom of the fresh food compartment.
Underneath the evaporator will be the "evaporator pan", or more correctly, the "evaporator drain pan".
When your fridge defrosts itself every 12 to 24 hours, the defrost heater comes on and melts all of the frost off the evaporator coil. The evaporator drain pan directs the melt water to a drain right at the lowest point of the drain pan.
Normally, the water drains through that drain hole and then follows a channel in the "evaporator housing" (which is below the evaporator drain pan). The evaporator housing directs the water to a drain at the back of the roof of the fridge's fresh food compartment or "refrigerator section".
That melt water drips into a cup and a small plastic tube directs that melt water to the outside at the back of the fridge, where another plastic tube carries it down to a receiving pan at the base of the refrigerator.
The heat from the compressor then re-evaporates that melt water into the ambient air. You can help dehumidify your house if you were to direct that melt water into a drain instead.
NOW, it's common as a barking dog to have the drain in the evaporator drain pan clog up with food and stuff that drops through the vent holes of the freezer compartment (which are the ones where cold air from the evaporator fan comes blowing into the freezer, and where air that's already gone through the freezer gets sucked back over the evaporator coil to be cooled again in a circulation loop. Both the incoming cold air and the outgoing warmer air will have their own vents. A frozen pea dropping down either vent can result in the refrigeration equivalent of a ball blocking up a drain pipe.)
The fix is typically to use a piece of stranded wire to clear the hole in the drain in the evaporator drain pan. Even a hash brown or a frozen pee that drops onto that evaporator drain pan will end up clogging the drain.
HOWEVER, if that evaporator drain pan drain appears to be clear, check that the melt water is dripping from the drain in the roof of the fresh food section into that little plastic cup that directs the water to the back of the refrigerator and down to the receiving pan around the compressor. If that plastic cup is clogged, the melt water could be over flowing the plastic cup and collecting at the bottom of the fridge.
On rare occasions it's possible that the entire space between the upper evaporator drain pan and the lower evaporator housing can be clogged with ice. This happens when either styrofoam part absorbs water and becomes water logged. In that case, that part turns into a block of ice, and any cold melt water that comes into contact with it refreezes again. If this is the case, the only fix is to replace the waterlogged part, and that can be a very big job indeed. In my 30 year carreer, I've only done it once.
I agree that it's a good idea to simply have a helper pour a pint of water into the evaporator drain pan, and see what the water does. If it spills out the drain cup high up on the back wall of the refrigerator section, that's where the clog is. If it pools up in the evaporator drain pan, it's drain hole that's clogged and the water can be coming out anywhere.
That post that says: "Frost-free" refrigerators have a tube leading from the freezer compartment out into the atmosphere (often towards an external drain pan at the base of the appliance.) This vents humid air from the freezer. If frost takes hold anywhere in the tube, it can quickly grow to block the tube with ice: and then the runoff humidity must go somewhere else, e.g. the bottom of the appliance.
The cure is usually to expose the freezer vent tube (often by simply removing the back panel of the refrigerator) and defrost it, e.g. with a hair dryer."
..is nutz. The freezer compartment will have a removable panel behind which are the evaporator and evaporator fan, but I have never seen a removable panel at the back of the fresh food compartment.
There is no "tube" coming from the freezer. There are styrofoam parts that are molded in such a way that they direct water to the drain in the evaporator drain pan, and then toward the drain at the back of the evaporator housing where the melt water drips out into that plastic cup. The only tubes there are are those that direct the water from the cup to the receiving pan at the bottom of the fridge.