We have had many requests for custom length mixing chamber tubes for the Plank automatic feeder. For any tube less than 12", please just message us after placing an order for your Plank, and add a note to the order with the requested size. If you wish to order a tube longer than 12", or a second/extra tube, select this product and add a note for the requested length. We recommend no longer than about 14-15", as anything longer than that risks fine particle foods sticking to the inside as it falls down to the water level. Please just contact us with any questions concerning custom Plank installations. Please allow a few days for processing & cutting on custom tube length requests.