Michigan State University Extension offers helpful advice on winterizing a sprayer.

Here are the tips:

  • Rinse the sprayer of all pesticide residue, and properly collect and dispose of the collected residue.
  • Clean and decontaminate the tank.
  • Inspect the sprayer. Check nozzles, screens, hoses, values and more. Verify the tank’s integrity.
  • Store the sprayer properly, ideally in an area that will not freeze.

Go here for the complete MSU article.