Estimation of the resident time

[MGV]

I would like to know how can I estimate a resident time to drain the water from an storage tank. Is there any equation or chart to do that?. I am recovering dead oil(16 API) so to desing the process I need to work out through the times.

 

[vintage70]

start with Bernoulli's Equation then v=sq rt of 2gh
also v(velocity) = Q/A (volumertic flowrate/area of orifice)
Q=V/t
t=V/A(1/sq rt 2gh)
integrate h1 to h2
solve for t
that should work