It's all a question of magnitude. You get ~ one atmosphere of pressure compliments of Mother Earth. This is approximately 33 feet or ten meters of water. If you add an open-topped column a couple of feet high, you're adding less than 10% above and beyond atmospheric. If you're borderline, that may do it. If you've got room for four feet, now you're around 12% of atmospheric. Note that the diameter of the pipe is immaterial (other than having strength to support itself).
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