First thing that comes to mind is increase the surface.
Second is to increase the heat, but that can go wrong via fire hazard or melting/evaporating/burning the product.
You could try creating a (partial) vacuum above the xylene, that would speed things up, but requires some specialist equipment.
Dont forget to ventilate properly,
xylene seems pretty toxic (and flammable)
I would keep pulling till nothing worthwhile shows up anymore. You get by far the most on the first pull, but perhaps it will be worth the effort/cost.