a device with a vessel for saliva that has one or more optical indicators to show the volume of saliva in the container . the optical indicators use the principle of total internal reflection together with the difference in refractive index between saliva and air . in embodiments , suitable visual indicators are either visible or invisible , when reflecting surfaces are either not immersed or immersed in saliva or vice versa . the device may comprise a vessel with a saliva pathway , a saliva containment region defining a saliva reservoir , the reservoir having a desired fill level , and an optical viewing window adjacent an angled reflective surface for level indication and / or validating a fill level . the device may include patient interface components and chemical test strips .