There are several ways of running vegetable oil. If I'm not mistaken, that is...

The two with which I'm most familiar:

SVO (Straight veg. oil) - Needs to be preheated in order to neutralize the glycerin problems.

WVO (Waste veg. oil) - Needs to be dewatered, filtered, PH balanced and made into biodiesel. This process separates the glycerin from the oil, so it doesn't need to be preheated first. However, will gel up quicker than "dino diesel" (that's kind of catchy), so winter running needs a mix of veggies and dinosaurs.

The PH does come from the cooking and such. Everything has a PH level of something, though, and it has to be correct. But the WVO does require much closer attention to the PH level and will always need to be adjusted.

I can't overemphasize the hazards of working with the chemicals that are needed to make biodiesel. Even just the fumes from methanol can kill you, and anyone who got a C grade in science class probably knows what lye can do to your skin, let alone your internal organs or mucous membranes if you should accidentally ingest it.

Oh, and to answer dieseldan's question, yes, you can use regular PH strips to test it. About the heaters, I think natural gas or an outdoor setup using wood scraps would work the best (and cheapest) I wouldn't want to think about what an electric heater would do to your electric bill... your savings would go out the window.