I live in New England, lots of road salt. But this winter I started getting this white sediment in my windshield washer fluid. It comes out with little chunks of white solid sediment and makes a mess of the windshield sides and overspray on the roof and sides of my car. I let it get down to maybe 1/3 full and added fresh washer fluid. It was better for awhile but started up worse again. I’m assuming there’s some contaminant in the container and/or lines that’s causing some kind of chemical reaction? It’s a mess - looks like the worst salted road spray on my car when there’s been no salted roads driven on. It started after I added a gallon of Prestone De-icing washer fluid (yellow) I picked up at a Family Dollar store - not sure if that’s the culprit but never had issues with that product before over the years. Help?
Remove the fluid bottle and clean it thoroughly, then reinstall.
If I had to guess, there’s a reason a bottle of Prestone fluid ended up at the dollar store, and it’s because it failed quality check so they didn’t want to sell it in normal stores.
Might be something in it that’s leeching crap out of your washer fluid reservoir, or the chunks might come from the fluid itself - perhaps they had something dissolved in it in a supersaturated state and it’s coming out of solution as it nucleates on random bits of gunk in the fluid reservoir.
I’d do what @MikeInNH said and then not buy that stuff from the dollar store anymore just to be sure. You don’t want that clogging your nozzles - that can be a pain to deal with.
Dollar store or similar places. They are what I drive by to get to a real store. Are they not the ones who sold China toothpaste with antifreeze in it?
don’t knock it til you try it. My teeth have never frozen up!
…or, it is a counterfeit, rather than a genuine Prestone product.
A few years ago, a new dollar store opened in the next town, so when I had some time to spare I decided to take a look at their merchandise. In the health & beauty aisle, they had “Colgate” toothpaste that had been made in either Kazakhstan or Uzbekistan (I forget which one). When I looked at the list of ingredients, instead of Fluoride as the anti-cavity agent, this supposedly genuine Colgate product contained…wait for it!…HONEY!
This toothpaste was almost surely a counterfeit item, and the OP’s WW fluid was almost surely also counterfeit.
And, to keep this on an automotive footing, last year the NJ Attorney General’s office ordered a seizure of the motor oil that was being sold at both Dollar General and Family Dollar stores. This oil was graded as “SA”, which means that it wasn’t fit for any car made after some time in the 1930s!
Honey!?
What a delicious way to get a mouth full of cavities, and it only cost a dollar! 
Almost makes you wonder if there were any dentists behind it to drum up some business 
Regarding the SA oil, would it be safe for lawnmowers today as long as it was (supposed to be) the correct weight?
I had the same problem with wiper fluid, and it was from a legit source. There was a lot of sediment in the unopened bottle that had been sitting on my shelf for a year or so. This was years ago, I think it was RainX fluid. I switched to Prestone at that point, haven’t had any more problems. But I look in the bottle just to be sure.
Sheesh, I’m in Minnesota and go through maybe two gallons of fluid a year. I just spend the $2 for regular stuff and wouldn’t ever think of eating, drinking or putting anything in my car from a dollar store.
Unfortunately at this point about all you can do is remove the container and fully flush it out along with the hoses. May not be so easy though since some of these are mounted under the fender. If that debris though is being sucked up by the pump, you may need a new pump at some point too.
Might be easier to place a garden hose into the reservoir neck and let it flush for awhile. Taking those out ranks right up there with a heater core.
Then suck out what you can with a turkey baster and then run the washer pump for a bit. Top off with generic fluid and call it a day…
I think OP and others have correctly diagnosed the problem, some sort of contaminate has found its way to the inside of bottle. How that happened, who knows? Doesn’t matter. Just do what’s required to remove everything in the bottle and replace w/fresh fluid. Next, make sure the filter cup that prevents any particles from getting into the bottle remains in good shape, if not replace it. Done.
I’ll add that here in San Jose I use a home-brew mixture of 20% ethyl alcohol and 80% tap water. Severe ambient temperatures that might freeze up such a home-brew mixture in North Dakota isn’t an issue here.
The owner’s manual for my pickup ('87 toyota) says that plain water is fine as long as you don’t reach freezing. I use the ‘Consumer Reports’ formula for window cleaner: 4 ounce isopropanol, 2 ounce ammonia, a few drops of dish soap, a quart of water. When I lived in the mountains it would freeze up in below-zero weather. I’d add some additional isopropanol. You can calculate the temperature any mixture will freeze at from the molal-freezing-point depression coefficients.
I agree with the comments to just flush the system out as much as possible. I’ve occasionally heard that you shouldn’t run the pump continuously when doing this because it’s not designed for this and it might overheat, but I don’t know if that’s true or not. You could have sediment clogging the nozzles, which you might be able to break up using a pin or paperclip if one of those fits without causing any damage.
The other reason not to drain it by pumping it out is so whatever is in the bottle doesn’t get into the lines. That’s even harder to clean out (many times you just have to replace them).