I can tell you if you are going to get a hazardous materials endorsement you better start the process now. They have to perform a backgroud check and it takes a while to get it. That is the way it is in Florida anyhow. One thing I will tell you is that if you do have placards on your trailer or tank, make sure you come to a complete stop at all RR crossings. Not a rolling stop. Don't even take a chance. Count to 5 then continue. If you are pulled over for not coming to a complete stop at a RR crossing it is so long license. It will be suspended. They are sticklers for the rules down here. Trust me, I know this happens I used to work for a freight company and saw it many times. I have seen many people loose there license and jobs over this. If it were me and I had purchased 50 gallons of sh and filled the rest with water (at least 125 gallon tank) I would placard it. It would be hard to prove what exactly was in the tank if you have more than just sh in there which most people hauling around that much product do. That is just not something I would want to be caught up in. Better safe than sorry. There are many laws about parking and paper work and someone staying within so many feet of the vehicle when it is parked. I would go ahead and study the book and take the test for the endorsment if it were me, just to be safe. One more thing, If you have enough chemical to placard then you better have a bill of lading with the un number, class, packing group, and emergency contact info. I am not sure how it would work if you have many different chemicals in a mix, but I would find out in my state if I hauled it around. That is one thing I am not sure about with water recovery systems. There is such a mixture with the recovery water that I don't know what you would do. I am not really sure how recovery systems work though.