the screen out invented by @HE_MAN works great (much better and safer than putty knife).
It’s even better and safer to unlatch and remove a screen from the inside so there is no need to pry at all
Sure…when you can. Some customers just want outs only and aren’t always home.
BTW I never recommend removing a double hung window, as most seem to have damaged hardware and getting the tensioners to reingage is an exercise in frustration. Granted we don’t have that type where I’ve worked in VA/KY, most are tilts.
That’s why I say we need inside access even if we’re only cleaning the outside.
Ya, we only tilt in if need be. Usually a third story hard to reach from the outside type of window.
The only screens I can’t remove from the outside are the old type with that loop that hooks onto a stud on the sill. Drives me nuts.
Some window screens are manufactured interior removal based. That means ya gotta open the window from the inside, remove the screen by pulling the screen towards you to take it out, then shut the window. They exist both on sliders and double hung windows. Most homeowners don’t realize it, and sometimes I don’t notice it right away; until I get close enough.
For the reason shown at the beginning I always spread large towels under the window I am working inside so as not to drip solution on the floor, carpet, or furniture.
Those screen tabs should be facing outward since the screen is removed from the outside, but over time they tend to be brittle or even pull out - up sell screen repair. 
Well, I tried to do the ‘tab facing out’ thing on a customer’s house, got a call back a couple weeks later asking me not to do that anymore.
Yes…screen repair! I do quite a bit, they REALLY appreciate the service, especially if they are selling the house.
