Defrosting from your owners manual

The cooling fins of the refrigerator operate at below freezing
temperature and will naturally form frost from humidity, which is
always present in the air. The humidity inside the refrigerator
increases:
- with higher outside temperature and humidity.
- with the storage of non-sealed fresh foods or warm foods.
- with the amount of time that the door(s) are open.
- with any air leakage into the refrigerator.
Although the refrigerator is not frost -free, it is made to limit frost
on the cooling fins. At regular intervals, the temperature control
system automatically melts most of the frost from the cooling
fins. The water from the cooling fins drains into a collection cup
that is attached to the back of the refrigerator. The heat of the
cooling system evaporates the water from the collection cup.
It is normal for frost to collect inside the freezer. Excess frost
decreases the cooling performance of the refrigerator. Defrost
the refrigerator and freezer as necessary:
- Remove all food from the refrigerator.
- Turn the refrigerator OFF.
NOTE: Defrosting the refrigerator makes excess water inside
the refrigerator.
- Remove the drain hose from the drip cup at the rear of the
refrigerator.
- Put the drain hose into a half-gallon or larger container to
capture water.
- Put dry towels (etc.) inside the refrigerator and freezer to
absorb melted frost.

On our Norcold it drains to a cup at the back of the refridg. It is supposed to evaporate but it doesn't....at least not fast enough, so it overflows and makes a real mess. I added a length of hose to go out the vent and drip on the ground (like the old rv fridges) and all is good.