A gray topped tube is typically inverted four to five times. This kind of a tube is used to draw blood to be used for lactate tests, glucose tests, and blood sugar tests, although there are other kinds of tests that could be done on the blood that was drawn. The grey tubes are inverted like this so that the additives in the tube can gently be mixed into the blood.
These additives are typically sodium fluoride - with or without an anticoagulant - or possibly potassium oxalate. Possibly both. These will allow the labs to play around with what the blood does during a test, so it’s often mixed up beforehand. Then, the phlebotomist just has to draw the blood and mix it up with the additives.
