Before accepting that smaller tubes are of equal drainage efficacy, another question should be answered. How could a smaller tube be equivalent to a larger tube? Flow of gas4 or liquid5 through a tube is directly proportional to the bore (diameter or radius) and inversely proportional to the length of the tube. Therefore, intuitively, a bigger bore tube should be better! Two authors of the current study provide excellent insight as to why this does not consistently hold true.6 Consider the reasons that fluid, in this case infected pleural fluid, may resist drainage through a tube. First, high viscosity fluid may impede drainage and block the tube, and in this case a larger bore may be of assistance. However, a smaller-bore tube may be kept clear in such a setting by periodic flushing, as is recommended by the BTS guidelines1 and is the case in the MIST1 study.3 Second, the balance of forces drawing the fluid through the tube may be inadequate. Provided that the suction force applied to the tube is not blocked, the balance of forces drawing fluid through the tube will remain adequate. The negative pressure at the tip of the tube (or side holes of the tube) is transmitted through the pleural fluid to the lung surface. Fluid flow is related to the balance between the negative suction pressure and the compliance of the underlying lung, not the tube bore. The speed with which fluid is drained may be improved by drain size (bore), but the chance of ultimate success remains unchanged. Speed considerations are important if fluid or air is being rapidly produced wherein a larger bore could be required to keep pace with production, as in a pneumothorax in a mechanically ventilated patient with a brisk air leak or in a traumatic hemothorax with rapid bleeding. If speed is not required, smaller-bore tubes suffice in pleural infection, and in other pleural problems, such as slowly evolving malignant effusions and static pneumothoraces. Last, in the setting of septated fluid collections, as the fluid is drained, the septae distort and distribute the drainage pressure across the locules and the lung surface. The pressure gradient across a locule wall predicts whether it will rupture and drain. Catheter patency and transmission of negative suction pressure predicts success, not the bore of the catheter.