The present invention is directed to a toilet that includes a slanted fill tube with an optical proximity sensor positioned on or within the inner surface of the fill tube. The optical proximity sensor includes an incoherent light source and a photodiode. The optical proximity sensor as disclosed herein detects small changes in volumes added to a toilet bowl. Consequently, small volumes of excrement that are deposited in the toilet bowl by a user may be detected with greater accuracy. In some embodiments, information about the volume of urine or feces deposited into the toilet bowl is recorded and calculated by a processor. Other sensors, including a toilet bowl water level sensor and a gas sensor may collect data in combination with the optical proximity sensor to provide more complete information about the user's health.