How do you drain a concrete inground pool in fl to prevent it caving in?

Concrete pools do not "cave in", however part of the pool can rise 2' above the ground. This is caused by hydrostatic pressure which exists beneath most Swimming Pools. As the pool is emptied, the weight of the water is reduced and, eventually, the hydrostatic pressure (underground water) is sufficient to lift a portion of the pool high enough into the air to eliminate the pressure. This can be easily avoided by removing the hydrostatic relief plug(s) as the water level drops. Concrete and gunite pools have some form of a relief valve underneath the drain cover. Pools 20'x40' and larger also usually have 2 additional relief valves. They are located on each side of the "steep slope" and should be removed as soon as the water level drops below them. As a final precaution, only empty the pool when it's not during the rainy season, unless it is an emergency. In most of the U.S., the fall, between Labor Day and the end of October, is the best time for cosmetic projects because of less ground water and less rain delays.