The diagram attached is a picture of the problem I have. I have a 10ft tall cylindrical tank with 20ft of pipe directly under it. The tank at full capacity can hold 100 gallons of water or 10 gallons per ft. I want to calculate the pressure of the water right before it leaves the pipe 20ft below. The pipe is of 1" diameter. I know from fluid mechanics that pressure=rho*gravity*change in height. Is it important to apply the diameter of the pipe into the calculation or is it negligible?? Thank in advance!!