Can you weigh the tank? Most sensors will not work through steel unless you can find an ultrasonic that clamps onto the tank.

Forgot to mention Turck Levelprox sensors but I don't know if they still make them.

No way to weigh,the silo is a size of 5 story building:)

Are you checking to see if the Settled Material is above or below a line?.. Can you use a bin shaker and check the Vibration to 'feel' if there is 'Weight' behind the Bulkhead.. ( Sonic? )

Cap

If you're not looking for an analog level, and simply want to know if the product is at a predetermined level, I see bindicators used in the woodworking industry a lot. They are simple creatures, and they have a few different styles. The unit can be mounted inside the silo or externally.

https://www.bindicator.com/

I think any of the Bindicator models will require a penetration of the vessel. If you can access the top of the silo, this product should work:

https://www.vega.com/en-us/products/product-catalog/level/radar/vegapuls-6x

Radiometric sensors can detect through steel walls but that is another can of worms cost and regulation wise. Vega Pointrac 31 is one example.

If you have access to the top, radar is a great option. The 6x is a great sensor.