How to liberate propylthiouracil
According to https://pubchem.ncbi.nlm.nih.gov, propylthiouracil has the following solubility properties:  


  1 part dissolves in about 900 parts water at 20 deg C, in 100 parts
  boiling water, in 60 parts ethyl alc, in 60 parts acetone; practically
  insol in ether, chloroform, benzene (emphasis mine); freely sol in aq soln of ammonia
  and alkali hydroxides.  


I would start with a small amount of your "sludgy" product. Stir it with ether as a first choice, chloroform as a second, for a while and see first of all whether you really get multiple phases or if just forms a less viscous sludge.  In a perfect world, after letting the solution set you would see the white propylthiouracil solid settle out at the bottom, with a sludge-discolored solvent layer on top.  If you see anything resembling this, then I would pursue this technique with more thorough stirring/shaking, maybe centrifuging to get better settling of your product, then further rinsing your product on filter paper with a vacuum flask, etc.  Try the other solvents if available if ether doesn't work.  The success/failure of this approach depends on the solubility of the sludgy stuff in the solvent.  It may fail, it may not give the purity you need, it may work wonderfully, but it is a cheap and simple way to test a method with a reasonable probability of success.