Oh, they'll clean it. Usually with a dirty rag out of their pocket and with a big ball of spit!
"Clean enough Sir?"
Did the good ole Canopy Cloth go out with the Lightning?
Anyhow, in my day it was a matter of our own self esteem and all-round diligence to ensure canopies and windscreens were clean (even when our turnarounds were usually in single digit minutes). Don't remember any wash bottle thingies in those days.