TSP is more of a detergent and works well in general cleaning. To kill mold and mildew use a mixture of 1 part clorox to one part water. You can also add TSP to this and a tablespoon of dish detergent will assist in better wetting. Apply to your siding with a garden sprayer and let sit 10 or 15 minutes then rinse well with water. If you have a dark stain or paint try on a small area to insure it wont hurt the paint color. This will last for awhile but to eliminate the problem a paint or stain that contains a mildewcide, such as Jomaps M1 will take care of it.