The installation of a water level sensor in the water tank was a whole different story.
First, there are different types of water tanks, made using different designs and materials.
Not all water tanks have an additional input for the water feed pipe. (Only latest generation water tanks have 2 inputs for left-side and right-side installation). Previous generation water tanks have only one input for the water feed pipe. Apparently, it was assumed that the water tank is installed and connected to the water once, and after that, it would not be reconnected ever again).
But even this was not the main problem. In the end, you can drill a hole in the tank top to mount the sensor.
The main problem was that the sensor has an M8 installation thread. The fixator for this thread is an 8mm nut.
Therefore, for simple and fast installation we need to make sure that the connector on the sensor goes through an 8mm nut. In this case, the sensor should be at least relatively waterproof and have at least 3 contacts. Otherwise, we would have to solder the connector after the sensor is installed, which is absolutely horrible idea, considering the place and conditions for soldering.
I could also redo the connection system of the water level sensor in the tank, but I decided to stay on a previous path.