Mildew wiper fluid

For some reason every time I use my wiper fluid, my truck cab gets filled with this horrid stench of mildew. Somehow the water has gotten nasty in my reservoir. I drained it all out and re-filled with clean water but it still does it. What are some ideas on how to clean this out?

 

Buy a couple bottles isopropyl alcohol, run the sprayer to get it in the lines, let it sit for a couple minutes, repeat a couple times and fill it with washer fluid. The remaining alcohol won't hurt anything and will mix with the fluid.

 

I ran a half bottle of alcohol through the lines and it worked. No more stank in the water. Then had to buy a $3.69 bottle of Prestone washer fluid but it doesn’t have any smell