why is coolant leaking from the rear heat/ac unit drain hose on 2002 Chevrolet Trailblazer

the car is a 2002 trailblazer, at first there was a small spot on the driveway, then after a month or so the car become low on coolant. I topped it off and looked under the rear of the car.
I squeezed the drain on the unit lightly and coolant poured out the hose.

Asked by for the 2002 Chevrolet Trailblazer