Spawning particles inside the mesh bounds

I’m trying to create a Niagara particle effect, which would spawn the particles uniformly within a mesh.

I’m able to spawn them on the surface of the mesh with ‘static mesh location’. I’m able to spawn them uniformly and then kill ones which are not fitting within expected bounds with ‘kill particles in Volume’, but it allows me to select only primitive shapes, not mesh bounds. Is there any way to spawn particles inside non-trivial shape?

I’m trying to achive dissolve into sand effect, by turning a mesh into a lot of yellowish particles and letting them fall according to gravity. Atm I’m not concerned if ‘sand’ itself looks very realistic, just want to play around with the idea - but unfortunately, putting particles only on the surface of the mesh doesn’t look that good.

I would also like to know how to do this.