Abstract: A refrigerator having a defrostable evaporator disposed in a food storage compartment wherein a drain system is provided for disposing of the defrost water dripping from the evaporator during a defrost operation. The drain system includes a drip tray disposed within the food storage compartment below the evaporator and an evaporator pan mounted below the food storage compartment. A drain tube is provided having a first end positioned below the drip tray for receiving the defrost water and having a second end positioned over the evaporator pan such that the drain tube drains the defrost water from the drip tray into the evaporator pan. The drain tube further includes a drain trap portion and a vent disposed upstream of the drain trap portion. The vent includes a valve for allowing air flow into the drain tube for equalizing the air pressure in the food storage compartment with the ambient air pressure but prevents air flow out of the drain tube such that no thermal leakage occurs through the drain tube.