The way that we have found to keep our windows clean is this:
After the morning PCM and finishing loading you car, before you leave the building, get the paper towels and window cleaner and start cleaning them. This aggravates management to the point that they will make sure your windows are cleaned every night. Try it.
Whatever you do, don't clean them in the morning on your time or the problem will never be solved. Besides, if you slip and fall off the bumper and get hurt while not on the clock, it could create a problem for you.