I cleaned an air filter in a sonic cleaner using water and simple green. I didn’t take photos before and after of the filters appearance, it was not a big change visually.
But, sure did end up with lots of dirt in the bottom of the tank.
This was the filter from my KT100. I have no idea how much time was on it. A friend was using the engine for enduro racing years ago.
Reminds me of being a kid, and the bottom of the bath tub after a full day of riding dirt bikes.