at the risk of causing a heated debate :

you cant do a particularly good job on any upstairs sills with a brush

its a trade off against the result you would get from wiping em down off a ladder,even after you rinse and wipe off there is often excess water leeching out from bottom of window frame and it can trail muck out with it,par for the course but most customers not that bothered on my round,just do good job on down cills and you should be fine
please note: this is my experience,other users experiences may differ
