I recently had to replace one of my central air / furnace units in my attic. While the old unit was operating on its last legs, it was dripping water from the "secondary" drain to the exterior of the house. This drain ends with a small PVC pipe sticking out of the bottom of the soffit on the upper floor.

The water that dripped from here had a tendency to drip against the house siding and windows on the way down to the ground. Those continual drops left a rust colored tone on each place it touched; the siding, the windows and frames, the downspout, etc.

I rinsed the areas with my pressure washer (no detergent, just water), but it didn't remove the rust color. Does anyone have any ideas what I can used to remove the rust color, especially from the white, metal window frames and the downspout?