My dad built a waste vegetable oil system for his 95 powerstroke 5th wheel puller out of essentially junk...and has been running on it for years.
Basically, he has a 60 gallon reserve tank in the bed. he has a 2-stage filtered gravity-feed funnel system he made to pour the waste oil into when filling to keep particles out. There is NO other preparation to the fuel performed. This is NOT bio-diesel, it's just waste veg oil.
At first, this is basically ALL he did...and later ran into some problems in cooler/colder weather. The veg oil and some of the animal fat solids in the oil started to solidify in the lines; making a mess.
The second generation solution was born. Now he has a plate-type transmission cooler in the bottom of his fuel tank and engine coolant runs through it. Engine coolant also runs along every length of fuel line that might carry WVO. Lastly, he has a temp gauge on the dash to tell him when the WVO is up to temp and safe to use. He was mixing diesel with the WVO for a while but stopped doing that...something about having the two seperate in the tank anyway.
He starts and stops the truck on diesel, and switches back to diesel well before reaching his destination...otherwise lets it idle on diesel long enough to clear the WVO from the system. He also doesn't switch to WVO until the entire system is up to temp. I suggested a temperature dependant interlock, but he prefers manual. Anyway, he starts the truck, lets it run down the road, then switches over to WVO once it's warm...and back to diesel before he shuts it down. He's been doing this since the truck had 15K miles on it...and it now has almost 250K on it and still going strong. Mileage is unchanged. Power is unchanged. One set of glow plugs and one set of injectors in 250K miles. He has a kill switch on the glow plugs...doesn't use them unless he needs them.
Anyway, that's one old farts way of saving money...and it works wonders. He brags that he makes it from Bend, Oregon to Yuma, AZ for about $5 in fuel cost...planning the route in advance from donut shop to donut shop. He has the whole route planned, and calls them in advance using his free minutes on the cell phone I provided. He prefers the smell (and taste) of donuts over french fries. He once filled up at a Fish and Chips Seafood place and said he couldn't eat seafood food again for like 6mos after that experience. 500+ miles of fish smell. Never Again. LOL