UPDATE July 2020: I was reviewing this post from 2015 and found that Steve’s website is no more. Here is a 2006 article about his rig, from the website of RV Business: Man Powers RV with Used Fast Food Oil

A powerful smell of french fries accompanied the big rig that pulled in beside us. Steve Adler and his family were on their way to go whitewater rafting nearby. He is a self-proclaimed tinkerer and retrofitted his motor home to accept waste vegetable oil as fuel. He gets his oil from fast food restaurants that are usually happy to give up their spent oil by pumping it out with a 75-foot hose. The Adlers drove across the country last year for $46.00 in diesel. The coach motor starts up with diesel, then he switches to the bio fuel. It still has a regular diesel tank, in case he can’t find an adequate fuel source, so as he proudly proclaims, “it’s a hybrid!” So far he hasn’t needed to use much in the way of traditional fuel.

In the interest of learning whether using spent vegetable oil in RVs was still a thing, and found this blog: Living Lightly in a Grease Powered RV It most certainly is still a thing.