A drain pump is used to move condensation away from the indoor unit when gravity drainage isn't possible. This is a standard feature in our Ceiling Cassette Multi-Zone units. The MRCOOL Olympus Cassette 24,000 BTU relies on its pump for reliable moisture removal. Without a pump, ceiling-mounted units would require complex sloping pipes through walls. These pumps are designed to be extremely quiet and reliable. They are essential for any installation where the indoor unit is lower than the exit point for the water.