I don't know about the state you are in, but here we have to take it to either a POTW, or you can take it to a coin-op car wash and dump it. Anyplace that would have a clarifier or oil water seperator, prior to discharge into the Sanitary Sewer. If you are cleaning gas stations, check with the gas station owner if they have a drive through car wash. They usually have clarifiers installed there, so you could dump it on site that way. Rather than transporting it. That opens up a whole new world and headache for regulations. All my flat work is done at new car dealers. So I can dump it into their clarifier on site; provided the contaminate levels don't exceed certain amounts. Hope this helps.