Yes, that black thing is the sensor.
Question? Are you changing them because you do not like them or because they do not work? They can be removed for careful cleaning as they do have a very thin clear membrane in them. Ours are accurate and I have cleaned them about every two years. Once calibrated, they do the job on all three tanks. If you have a bad one, they can be purchased direct from he manufacturer cheapest at www.catconproducts.com and look for RV-Sensor. Catcon may also have a level gauge available that could be installed right in the bay. Just another thought.
Hope this may help a little. Have a great day Dennis. Happy Trails Bert