Math question.. SOLVED!

So, our good friend (Laci) took it upon himself to answer our math challenge. We're very grateful that you helped us solve this one. It took some googling however he found a good calculator online to solve this question. So according to him to empty the tank from a 92cm water level to about zero would take 2 hours 54 minutes. Our tank is actually higher, however the outflow pipe is below the top of the slab of course so from the pipe bottom (upper water level) is only 92cm.

Thanks again Laci for the numbers.

Our next challenge will be the time it takes to fill this tank based on average rainfall here.