I have a job exactly like this. She has had me clean her windows for going on 4 years now twice a year. And there are 5 exterior panes I JUST CAN NOT REACH - they are nearly 3.5 story. Not only do I only do second story or less, even when I push my limits these I just can’t reach as they are above a really slanted driveway and I need a 30ft + ladder to get the right safe angle.
They are FILTHY. Well I got my wfp setup this year and really wanted to get they ears of bird crud and others off. So first I pure water rinsed them, then I made a typical solution of my dawn water mix and proceeded to use my bronze wool wfp attachment and scrub away, after that I gave a quick rinse and used my Tucker brush to rub in more, (still slightly soapy which is what I wanted) then rinse twice and damn they look beautiful!!!
This is all just my opinion, thank you.