Thanks for the link but I think their estimates are very conservative. According to my calculations from their chart, using cross section area a 2" circle will allow 6.8 GPM thru it, and a 3" hole will allow 15.2 GPM. Does this sound right
I'm looking for a chart that would give me gravity flow of water thru different size circular openings. for example. I have a 500 gal tank with a 2" hole in the side. What gpm flow can I put in the tank where the water level in the tank will never rise above the top of the hole. Please help