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.