I have a water tank that is 24' tall. Water flows from the bottom of the tank thru a 8" plastic pipe for a distance of 650' down a hill for a elevation drop of 70'. What would be the expected water pressure at the bottom of the pipe given a flow of 20 gallons per minute? I've researched several books and they say to use the Hazen-Willams formula. Can somebody help me work thru this? Thanks!