Hi Les. I'm Cindy / Justice? Mix a half-cup of baking soda into a gallon of water. Add one-eighth cup liquid dish soap. Spray this solution on your concrete and let it sit for 30 mins. Then scrub and rinse. For heavily stained or mildewed jobs, you may need to use a pressure washer. Good luck Les.
Cindy, thank you very much for the tips.
Pressure washer using Krud Kutter from Lowes works great for us.
Thank you for your advice.