Symptomatic chronic subdural hematoma is a prevalent conditions among the elderly, making burr hole surgical evacuation a very frequent cranial neurosurgical procedure. Recurrence of chronic subdural hematoma requiring revision surgery is associated with higher morbidity and mortality. Decreasing postoperative pneumocephalus is a simple but helpful mean allowing to reduce chronic subdural hematoma recurrence. A few years ago, our team has already described the use of the subdural drain to fill the subdural drain with saline, thus helping pneumocephalus out. Zhou and colleagues present an ingenious system using fluid mechanics principles, with an opened syringe connected to the subdural drain and held above the level of the burr hole in order to make saline flow into the subdural space; then held below the level of the burr hole to make pneumocephalus out, the remaining saline acting as a one-way-valve like the drainage bag of a pneumothorax. Nevertheless, in order to optimize this system, the burr hole should be placed in the horizontal plane at the highest point of the skull to be able to fill the subdural space with saline completely.