I'd like some advice please on the best way to calculate the volume of a tank as it increases. It's necessary for me to determine the volume of the tank as it fills every vertical ft (i.e volume when 1ft full etc).
Here is a cross section of the tank, showing its dimensions in feet:
No real trigonometry involved.
You shoud be able to compute the area of the trapezoid (can be seen as rectangle on the left + triangle) and that of the rectangle above it.
When the water flows, the area first grows linearly until the trapezoid area is filled, then it continues to grow linearly, until the rectangle area is filled.