The present invention provides a beverage maker having an in-line heating assembly for heating water to make hot beverages such as coffee and tea. The heating assembly defines a flow path that runs past a plurality of heaters for heating water to a desired temperature. In this manner, the beverage maker heats water as it travels, alleviating the need for a water tank or vessel, resulting in increased savings in weight and size, as well as reducing brew time. Additionally, an optical sensor assembly is provided to detect when a serving container of the beverage maker has a prescribed capacity of liquid within it. The sensor assembly includes at least one light source aligned to shine into the container and at least one detector aligned to detect light reflected off the liquid surface within the container. A drainage assembly is also provided that can drain liquid through either a connector port into an airplane's wastewater system or through a drainage port into a drainage sump.