An opening, usually at the floor of the pool, or close to it, that draws bottom water, for the pump and filter. Important for good circulation.SEE ALSO "HELPFUL HINTS"

Main drains and suction lines SHOULD ALWAYS have cover in place when operating! Hair, clothing, arms, legs, appendages can be trapped by suction in main drain! Too many people have died from being trapped by sitting on the main drain and drowning because the suction area was completely covered, creating a vacuum seal that prevented the person from simply standing up and getting to air. and with some children, the suction has actually disemboweled them! If a new pool construction, TWO main drains should be installed side by side (same line to equipment, just split a couple of feet apart to help prevent one from having as much suction at the opening).