There are a couple of hints that increase the accurancy of the measurements on the drainage bag. Firstly, some nurses are unaware that it is necessary to put the bag onto the drain before vacuuming it. This is because air is then pushed into the bag, which separates the plastic sides of the bag, and allows the exudate to settlle evenly. Secondly, it is helpful to leave the drained fluid for 15 minutes or so after vacuuming the system, so that the exudate will settle.