Hi Dan & Jan, Pipe is not a good vertical outlet for bees, the inside is too smooth and straight. A better choice is flexible dust collector hose which comes in 2 1/2" and 4" sizes in both clear and black. It can be shaped as a spiral round a vertical post, thereby reducing the degree of the slope involved and the vinyl provides a stickier surface than ABS or PVC. The more turns in a spiral the more the slope is reduced, and the longer distance they have to travel. The longer the distance the larger the diameter you should use. - Black is less distracting for the bees, they don't get confused by the light - Clear is better for observation, and with time the bees will figure out how to ignore the light coming in the hose. Woodcraft and Rocklers are a better place to buy than Home Depot or Lowes. Enjoy, JP -- Visit www.honeybeeworld.com/bee-l for rules, FAQ and other info ---