To calculate the PSI (pounds per square inch) at the base of the 20" line in your tank, we need to consider the height of the water column above the base of the line and the properties of water.

First, let's convert the diameter of the tank from meters to inches for consistency. Since there are 39.37 inches in a meter, the tank's diameter is approximately 1181.1 inches (30 * 39.37).

Next, we'll determine the pressure exerted by the water column. The pressure at any given depth in a fluid is given by the hydrostatic pressure formula:

Pressure = Density × Gravity × Height

In this case, we'll use the average density of fresh water, which is approximately 62.4 pounds per cubic foot. To convert this to pounds per cubic inch, we divide by 12^3 (12 inches in a foot).

Density = 62.4 lb/ft³ ÷ (12 in/ft)^3 0.03613 lb/in³

The acceleration due to gravity is approximately 32.2 ft/s². Now we can calculate the pressure at the base of the tank using the height of the water column:

Pressure = 0.03613 lb/in³ × 32.2 ft/s² × 17 m 19.39 lb/in²

Therefore, the pressure at the base of the tank is approximately 19.39 PSI. This value represents the pressure acting on the 20" line.