Xylene can completely ruin a freeze precip.
The xylene here could in principle be removed by adding some heptane, then separating off the NPS. That way, any remaining xylene/heptane mixture will contain less of the stinky xylene than before. Any remaining heptane will evaporate more easily than xylene would and some of the xylene it contains will evaporate at the same time. This can then be repeated with fresh heptane.
If, as it seems, you're having trouble separating the NPS from the water solution, using a vessel with a much thinner neck will facilitate this. Optimally, a separatory funnel would be used for this procedure but not everyone will have access to one of those.
βThere is a way of manipulating matter and energy so as to produce what modern scientists call 'a field of force'. The field acts on the observer and puts him in a privileged position vis-à-vis the universe. From this position he has access to the realities which are ordinarily hidden from us by time and space, matter and energy. This is what we call the Great Work."
β Jacques Bergier, quoting Fulcanelli