Because the companies that they sell it to (or that they pay to take it) can "penalize" them if the wrong stuff is in it. I think if there's (too much) anti-freeze, they can't recycle it and the entire batch has to disposed of as hazardous waste. In the past, some places would let you dump it in the tank yourself but none of the parts stores do that anymore. At O'Reilly, you go to the back door and you can help carry them in, then sign the form. The guy will sniff the contents before dumping it in too.Just FYI, the auto places are more diligent about looking for contaminants in the oil.
Why did you use the original containers for the used oil? That's kinda like filling empty beer bottles with your own....never mind.
For clarification, I usually use a large 4(?) gallon container that has a screw-on lid, but I've been using the jugs lately because I've been mixing in tiny amounts (an ounce or two at a time) of really stale gasoline to get rid of about 1/3 of a gallon I extracted out of a gas tank replacement job we did on a truck that had been sitting for an eternity. "Fuel dilution." I figure tiny amounts are in used oil anyway. To my knowledge, nobody in my area deals with recycling/properly disposing odd chemicals, so it's all I know to do to keep it from going somewhere really bad like the trash, wastewater drains, etc (I would never do that). At least they are used to dealing with fuel dilution. If it was a larger amount, obviously I'd have to take a different approach, but it was 1/3 of a gallon.
The original containers are absolutely ideal for storing the old oil. They're the right size, they're available, they have secure lids/caps, etc, etc.Why did you use the original containers for the used oil? That's kinda like filling empty beer bottles with your own....never mind.