A:Answer I bought this unit specifically because the drain line is optional when running only AC, and it has an internal tank. I live in an apt on the 11th floor and have no option to run a water hose outside. For the first few days of operation, I never got a ‘Tank Full’. Indication, but it also didn’t cool the room much. My room is only 440 sq ft, but this is in Honolulu - warm, humid, and my room faces the sun. After a few days I was pretty frustrated, but decided to hook the water hose up, which helped cool the room an additional 5-10 degrees, maybe more. But now I have to empty this 10 gallon trash bucket 2-3 times a day.