Use this optical sensor from Sensata Cynergy3 to detect the presence or absence of all types of liquids. It consists of an infrared emitter coupled with a light transistor and a sensing tip for efficient detection. When the tip makes contact with a liquid, the infrared light escapes due to refraction, reducing the coupling and triggering a detection signal. This sensor is made of polysulfone thermoplastic, which can withstand exposure to hot liquids. You'll find this type of sensor used to control liquid levels to prevent overspill, as well as to detect leaks.

• Maximum operating pressure of 7 bar for use in heavy-duty applications
• Polytetrafluoroethylene (PTFE) wire sheath for protection from corrosion and electromagnetic interference (EMI)
• Cable length of 250mm for ease of connection in tight spaces
• Resistant to false triggering caused by foaming for more accurate detection

This sensor can be installed on either the side or bottom of a tank. Drill a 12mm hole on a flat surface, ensuring it's free of burrs to prevent leakage. You can then either insert the device into the hole or screw it into an M12x1 socket.