ahhh, sorry mattsn, didn't se this until now, the first place I tried was journeytoforever, but it was bad, then on here there's a website called biodieslecommunity.org, or com, not sure, they helped out a lot to, but here's the proess ion a nutshell.
1 liter of used/unused oil
4 grams NaOH (sodium hydroxide=lye) or 1.4 times as much KOH(potassium hydroxide=also lye), try not to touch it too much
1/5 of a liter of methanol, and you need methanol, not ethalated methanol or methalated ethanol, it's gotta be pure, DO NOT screw around here, very dangerous, and I mean super dangerous stuff, really, blindness, death, and really explosive, ventilate wherever you're working
heat your grease to about 60*C and begin mixing. In a seperate, sealed container measure out the lye and methanol, limit the time exposed to the air because both of the chemicals are very hydrophilic, which means they take the water out of the air and mix with it, rendering them worthless, put them in a PET bottle, like a 2 liter bottle of coke, the lye should come in white pellets, when mixed with the clear methanol you now have methaloxide.
introduce this methaloxide to you grease and allow to mix for around 2 hours, maintain heat.
after this stop mixing and heating and wait a day, you will see a lighter probably milky fluid on top and a thick nasty lookin jank at the bottom, on top you have unwashed diesel fuel, on the bottom you have glycerin (bad stuff, be careful) get the glycerine out and if you have a compost heap it's good to use there.
Then you must wash the diesel, put 1/3 the quantity of fuel's worth of water in and mix, thoroughly, what you're doing here is introuing water to the fuel to ake out any remaining lye or methanol, beings that they're both hydrophilic, well you get it. After mixing allow to settle out, repeat this 2-3 times.
This step takes care of two things, if you have a bad reaction then you will get excess amounts of soap after this step, it's a solid-like white substance that forms when water comes into contact with unconverted tri- di- and mono-glycerides (unconverted grease) if you have this, then you did something wrong.
After washing three times allow a couple days to dry, this allows the water to evaporate leaving you with nic usable diesel, on the 7.3 forum there's a biodiesel thread that will help some too.
If you've used used grease, then you need to titrate to determine how much lye to use, check on the website for information about that
any larger size batch will use the same substance ratios and I didn't list any materials to use as vessels because that's all about what you have available, but at biodieselcommunity check out the appleseed, it's probably the best easiest way