If you are going to run a mobile car wash you will need to make sure that you do not allow water to enter a storm drain, as that is illegal and those drains are meant for actually rain water.

Blocking storm drains is easy and then allow the water to evaporate a little and take what is left in the waste tank. Next you will want to make pre-arrangements to get rid of the water for instance contact the city or make a deal with a Coin Op car wash to dump the carwash waste water there which will go into their system properly.

Or you can divert the water if possible into vegetation and that should comply with the NPDES permitting, but be sure to run this by the local water quality control board or city.

One of the easiest ways to collect the wastewater is to dam up the flow towards the storm drain or block the storm drain completely. You can buy a vacuum, which both sucks and pumps the water from a Wal-Mart for about $79.00 and attach a garden hose to it to suck up any collected wastewater. Then you can put it into a small storage tank on your pick-up or trailer unit to remove it from the property.

There are other solutions also, which may include using a mat to wash on and there are a few companies, which sell these;