Then your technique is flawed. Have some residue left over after a cleaning? Use a waterless wash towel and go over the glass again without the use of any additional product. Streak free glass every time.
As for designing a product, not sure if it was already mentioned or not but how about a little rubber hose attachment that when you're pool rinsing, the metal shut off valve is not the first thing to touch the paint and instead, you have a more paint friendly rubber compound.