Good to hear you are going to try the gasoline blend idea. I assume you mean by 30% the 70% will be diesel fuel. I think that is a really wise, and cautious way to explore waste-oil-gasoline blends; however, there is a relationship between any waste oil and gasoline that should be maintained, which is about 20% gasoline to 80% waste oil. You could still run that blend at only 30% to diesel fuel, and your engine probably would not have any change in performance at all, and the gasoline content would only be 6%, which is to small for any diesel engine to notice, especially when in relation to waste oil at 20-80 parts.