One of the first things that went wrong with our E86 when we got it was the windscreen (and headlamp) washers.
Following advice on here, I carefully removed the tank completely (tricky, fiddly and i grazed my knuckles) and the two bits at the bottom with the filters were just completely covered in slime. I've never seen this in 20 years of car ownership! I nuked it with everything I could think of including bleach, but a year later the same thing happened again. The car spends a lot of time just sitting around which doesn't help. The second time was even with a strong quality screenwash mixture in the bottle.
From the service history, the previous owner also struggled with this!