Fast food restaurants are not a source for "good" oil. Oriental restaurants are better (but not always). Check out the various websites for more info. After all, Rudolph Diesel originally developed his engine to use "alternative" fuel. He believed that the farmers could "grow their own fuel".
There is a guy over at http://www.skoolie.net
that is running a skoolie (diesel) on waste oil. I think he is using a greasel setup (pre-warmed straight waste oil injected into hot engine) but I may be wrong (or there's more than one doing it). We attended a Bio-Diesel seminar at a local organic farm and decided it was too much hassle for someone who moves around alot. We would need a cargo trailer just to haul the unit around. Also there was the problem of finding waste oil and jet fuel (components for making bio-diesel). Here locally, we have found that #1 most restaurants dump their waste oil into the grease drains (which are then pumped out by a big truck along with some of the regular waste water) and #2 restaurant employees are not inclined or are incapable of learning to seperate the oil. #3 Some guy has "contracted" with the majority of the local restaurants to collect their waste oil for a bio-diesel plant that he is building.
When we are farther along with our bus conversion, I will look into the Greasel
setup again and check out the availability of unused vegetable oil from restaurant supply companies. I think it would be easier for us to obtain fresh drums of veggie oil from outfits like Sysco than to have to search out sources for good oil in the various towns we may travel thru and then have to strain the goop out.
For more info on running Straight Vegetable Oil (SVO) check this
BTW, the engine we will be usng is a standard (old) 8V71N Detroit Diesel with out any of the fancy computer stuff and we are leaning toward fresh, unused rapeseed (Canola) oil. We have the "souped up" N65 injectors on the engine but I don't think those would have to be changed. As far as the fuel taxes... most states do not have a system in place for collecting taxes on the alternatives fuels and therefoire it falls into a "loophole". Others that do have the tax exempt anything below a certain amount, usually more than enough for personal use (kinda like making homemade wine & beer).