Considerations:
I am trying to detect if the dustbin is full. The dustbin is a rectangular shoe-box like structure without any lid. The kind of material that will be collected will be mostly hair, paper, carpet etc. I am thinking to use optical sensors. But I do not want to go through the pain of cleaning sensors again and again.

1. Are there sensors that can be put in a glass case and they can penetrate through the glass?
2. Is there a better alternative then optical sensors (IR, depth, laser,weight, acoustic, capacitive, touch, limit switches ).
3. The system needs to be robust.​

Weight sensors: seems to be unreliable because the weight is not consistent.
Touch sensors: The material, say paper, if it touches the sensor then we can think the dustbin is full. But because dustbin is long (not cylindrical), the indication can be false. Also, in case of hair, the weight or touch, neither can help in detection.
Multiple IR sensors: These can be mounted and based on blockage, we can detect if the system is full but again I want to eliminate the need of cleaning sensors again and again.

 

I would use the optical sensors usually installed across the bottom of garage doors as a child/pet safety beam.They are modulated IR, and have good immunity to ambient and industrial lighting. They come complete with optics that make a narrow beam. Look at post #4 and #8 in this forum thread.

I have picked up two-pairs of the TX-RX at my local Habitat for Humanity Thrift shop for a couple of bucks. Otherwise, you can buy new ones on Amazon.

 

infra red leds will shine through glass or plastic, ultrasonic sensors may need cleaning,capacitive sensors could work,