oil based paints, paint strippers, used motor oil, drain cleaners etc.
these are normal products that every house will have that will become the 800 pound gorilla on your back when you try to take them to the dump or transfer station.
Our county recycling center has a special semi trailer setting there on the grounds for "hazmat" drop-off's, which is the stuff listed above. They contract with a company to properly dispose of this stuff. This is a free drop-off for county residents, might check with your neighboring counties.