Knowing how to clean double hungs from the inside is a huge plus!
I usually use my WFP and / or clean everything from the outside, its more time efficient
Every once in a while though, there's that one window that you just cant access safely, so shuffle them up and down and get them from the...
Pre-scrub and squeegee it, let it dry, then take a separate, dry strip washer and soak it with Zep or Sprayaway, scrub and squeegee again, then wait til it dries and detail the edges :)