A viscometer tube includes a tubular body divided into three sections: an upper feed section, a lower capillary section and an intermediate transition section providing a transition between the upper feed section and the lower capillary section. Liquid flows from the upper feed section to the intermediate transition section and then to the lower capillary section. The upper feed section intersects the intermediate transition section either laterally or from below. An upper remote end of the intermediate transition section is open to atmosphere.