Seat rail and vent cleaning?

Hi,

Sooo, as the result of a unfortunate event I seek help and advice here.  I was transporting about 50 kilos of small pea gravel in the back with the seats down.  Despite knowing the perils and being extremely cautious, I was cut off on the freeway and applying full brakes the container full slid and exploded resulting in a waterfall of gravel in my lap an floor!!!!!

I managed to get it all cleaned out, but know my seats don't slid in the rails and the back air vent was filled with the stuff.

So, my question; how do I go about removing and cleaning out both?

Ant help or advice is much appreciated.