Do you leave the catheter bags open? - 'cos it wouldn't take much of an air leak to fill one and then your valve will cease to work. If you leave your bag open won't any fluid leak onto the floor? An under water seal drain is safe, cheap and effective, and has none of these disadvantages. We take one Xray prior to drain insertion to confirm the presence of pneumo/haemo (unless there is a tension of course), and then watch the drain. Once it has stopped bubbling and swings less than an arbitrary 6cm (say 2 inches) we listen to the chest, if clear remove the drain and send the patient for a check Xray prior to discharge. Many folk are in 24 hours only. The walk to X ray dept is good physio! This is more or less the policy in most South African hospitals and it seem quick cheap and efficient. Obviously drains for non trauma reasons can be more tricky as the underlying lung is pathological.