Find the volume of the cylinder and divide by 2:
V = pi * r^2 * h
V = 3.14 * 11^2 * 17
V = 6458.98
Divide by 2 since it's half full:
6458.98 / 2 = 3229.49
Now divide it by 46.2 to see how long it will take to drain out:
3229.49 / 46.2 = 69.902
So it will take approximately 70 seconds to drain out.