I'm not a chemist, but by analogy with anaerobic bacteria we have on Earth, some of which produce methane gas, one could imagine something that expels silane gas.

The idea that we have "no idea" what life could look like out there in the universe is grossly oversold. We actually can put a lot of bounds on them, using rigorous mathematics, and discuss them despite not necessarily knowing all the chemical details.

That's basically ash, think of a coal burning plant and how they deal with waste.

Or iron smelting, how they leave the waste slag behind.

It's difficult to see how this could be made to work for a life form, because this is a very macroscopic process. On a microscopic level, well, we're all just ugly bags of mostly-water so we do it by suspending things in our mostly-water. As I understand it there are few to no good candidates for a silicon-friendly liquid base when you work through it.

(Interestingly, I have seen some suggestions that there could be other liquids that carbon-based life could be based on, such as ammonia. That said, it may not be coincidence that water is still almost certainly the best (accounting for the possibility that it's just the observer effect), and that's what all life forms reading this for the forseeably future are based on.)

If they are like humans they would emit a 1 to 2 KG bone every day.

Glass is pretty inert though, I wonder how it would decay/decompose.

into beautiful alien beaches, around tidal oceans of ammonia.

To this alien the glass would be gross and icky.

Do you have any sources that discuss this?