I should be able to do this, but its been a while and maybe I'm making this more difficult that it should be. Assume you have a cylinder nearly sealed but with an outlet hole at the top. I want to pump a fluid into the canister, pushing the air out of the hole, and time how long it takes. The ultimate goal is to try and see what size the hole is, or even what its flow coefficient (if flow rate Q = Area*velocity*K) What is the simplest way to go about this calculation? I have attached an image, the outlet hole can go anywhere. Lets say that I can control the pump's flow rate or pressure, and the air starts at 1atm both inside and outside. What is the best approach? By work done? By number of air molecules escaping? By force balancing? Thanks! Any ideas?