Dilute any excess detergent that you have and use it to water the garden. The detergent is not harmful to plants, but should not get into the waterways. Make sure your garden does not run off to a storm water drain and if it does, use a different way to dispose of the detergent.
Take the detergent to a local car wash or recycling plant. Recycling plants have special machines that recycle hazardous waste safely and without damaging the environment. Car washes will also have special tanks which are used to store and even recycle waste water full of harmful detergents.
Give the detergent to a neighbor or friend who will use it. This is a simple solution when you are making the switch to eco-friendly detergents. Just make sure your friend also knows how to recycle the detergent safely.
Check with your local water treatment plant or the U.S. Health department. If you are unsure what to do with your detergent or want to know if it is environmentally-safe, you can call your local water treatment plant or the U.S. department of Health and Human Services. They have information on all the detergents on the market and can advice you on the best ways to dispose of your detergent in your area.