Problem of Transient draining of Tanks

There is a unit mismatch in function H

Guess it should rather read

In the plot at the end you should not use the desired units in parentheses. 

If the plot should be shown in standard units (which are seconds and meter in your case anyway) its not necessary to do anything:

To show the units you may either use the labels or divide by the desired units:

That kind of division is necessary in case you don't want the plot shown in default units.

Here is the same plot using minutes at the x-axis and feet at the y-axis:

The difference lies of course just in the scaling of the axis.

MC15 file attached