I have a foul smell in my washer fluid reservoir when I have stale summer washer fluid that uses no methanol in it. I think it is an organic compound that goes sour and smells like puke. So the only way to deal with that is to just use water in summer, or change washer fluid before it has a chance to sour. Summer fluid I have used also gets particles forming in it making me wonder if the pump screen would get clogged and make the pump not pump, but that has never happened.