How do I determine the amount of time taken to empty a large tank full of water?

The tank should be empty in about 2-1/4 hours. Variables: h = elevation of tank D = diameter of tank A = orifice area (ft2) G = gravitational acceleration = 32.2 ft/sec2 ∆t = time required to empty tank (sec) The following formulas are based on turbulent flow of a Newtonian fluid through an outlet (orifice) in a tank.Explanation:Measure the number of liters or gallons in the container, and divide that number by 15. This gives the flow rate in liters per second or gallons per second. The formula is F = V/T, where F is the flow rate, V is the volume and T is the time.=180 s=3 min.