its easy, filter old oil, add parrafin or kerosence to get it thin enough, filter, mix with 50/50 diesel, now thats simple way, i used to filter mine a lot with magnets in filter as well, very mucky to do on a big scale, if i was doing a odd gallon of old oil easy.Now if u add it to red it goes black but you could still get done.Unless you could argue it was an aditive and there is no regulations i dont think of how much aditive u can put in fuel.

Thanks friends for all the advice I will take it and use it and feed back my experience when I decide which way to go so if I cock it up at least no one else will thanks again guys