Not good advice.

Shops are very busy and don't want to deal with non profit producing "customers" / low margin customers. If someone would have tried that at my shop, were told in no uncertain terms that I'm not interested and they persisted, the police are not far away.

In some states, there is a chain of doccumentation a shop must adhere to showing that any waste was properly disposed of. A shop can be held liable for improperly disposed waste taken be another party even if they gave it away. ( RE: if there was a huge oil spill at your house and the law said we will go easy on you if you tell us where you got the oil, would you keep quiet then go to jail or tell them where you got it and get probation? )

In the 80's shops got paid for waste oil, in the 90's they had to pay and now some areas are paying again. Why would a shop give a profit center away and have to use non productive time that costs them $$ ?

And there are huge fines ( Like $ 10,000 ) for running "red" diesel as it isn't taxed for road use. The same will apply to any untaxed fuel as the taxes go towards building and maintaining roads.

Regardless of all of this, burning used motor oil and ATF is a bad idea, neither are designed to be burnt and leave ash deposits. Used motor oil can be acidic, do you really want to put this through your injector pump?