[RyanH]

For the black streaks, I use Purple Power applied through a ShurFlo or pump up (butyl based automotive degreaser, like Pam's mentioned). There are other brands available through various distributors....Zep makes a purple cleaner (at home depot), various janitorial places servicing kitchen supplies will sell it as a degreaser. PP costs about $8 for a 2.5 gallon container from Auto Zone. If you want to avoid pressure washing them, brush it on (I use full strength) and rinse off. Don't allow it to dwell longer than about 30 seconds as it could degrade the integrity of the paint. It will usually make windows ugly when it gets on them, however, and they will have to be cleaned.