2011 forester washer reservoir contamination

[Michael103063]

I bought this forester almost a year ago. Ive added washer fluid but never pulled the dipstick out. When I did I found this oily sludge on the dipstick. I’m guessing somewhere along the way someone dumped something other than washer fluid in there, obvious I know.

Anyway, what’s the easiest way to flush this gunk out before it gets sucked into the nozzles and smears the windshield. It must be floating because the washers work fine (no oily residue on windshield)

Do I need to remove the entire washer bottle?

Thanks in advance.