calculation for hydropower project

Question

I'm studying a hydro-power project in high rise building. given a 100 story building(3 meter per floor) with 2.5 cubic meter of water per floor DAILY with 1 or more tanks within the floors and turbine at the ground. goal is to have the highest output per day with the minimal size turbine to save on the turbine cost. up until now I have few equations such as Potential Energy in a Tank or Reservoir and output of hydro-power turbine. I am missing a few equations and contents. formula of Time to empty a water tank( does the height of the water tank from the floor effects it),I've some online but none of them were direct and straightforward. does the water velocity formula exiting the tank of (2gh)^0.5 is based on the h of the tank or the ground? In the formula of hydro-power output(Pth = ρqgh), I'm very focused on the Q. I calculate it based on va(velocity and cross section of pipe) but I don't understand how the flow rate(Q in litter/sec) in the pipe at the has nothing to do with the falling height(water head above ground). please ignore the economical feasibility issues of the project. thank you very much for the help