Switch Between Paint and Sealer for Sprayer
If you want to switch back and forth between oil and latex products, it is best to have a separate hose for each (as per Graco).  


  Graco sprayers, hoses, guns, etc, are designed to be compatible
  with all of these types of fluids. There are a few other
  considerations that you should be aware of. Be sure that all equipment
  is of sufficient size and of a high enough pressure rating to work
  with the material that is being sprayed. Another issue to be aware of
  is that no matter how well a sprayer is cleaned out, some residue will
  remain behind. It is not uncommon to have pigmented paints contaminate
  a clear coating like varnish and lacquer. Switching between
  water-based and solvent-based materials can also make the insides of
  the pump gummy and sticky. Ideally, we would recommend two different
  sprayers, but at the very least, you should use a dedicated hose for
  lacquer and clear coatings.