Many of us have been disposing of our wash water by either pouring it out on the ground or down the sewer. The "Man" is likely to have a cow if he finds out you are doing that. If any gets into a stream or goes down a storm drain, then your in violation of the clean water act. If you pour it down the drain on a city sewer, you are probably overloading the system and causing the waste water treatment plant to get fined by the federal government for discharging untreated sewage.

The wash water contains both soap and biodiesel. The soaps are heavy in carbons, which demand large amounts of oxygen to biodegrade. The term to describe this is Biochemical Oxygen Demand (BOD). Typically the wash water from the first wash will usually kill your lawn. If you use NaOH, the second and third washes will also kill the lawn. One way to reduce the BOD is to let the wash water settle in a drum for a week or so. The biodiesel that was bound up in the soaps often rise to the top and can be used for fuel.