Step 4Filter the grease
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Basically what your gonna try to do is strain out all the little pieces floating around, I tried lots of filter methods. You can spend money on filters made for this but i found using a piece of thick cloth used as a screen over a bucket can work fairly well, it just might take a few times going through depending on what sort of fabric you use, but feel free to try other filtering methods. This can get messy but you'll learn techniques soon enough and will have it down to an art.
For practical effects, you can add WVO (filtered of course) blended whit diesel to a diesel vehicle, BUT NO MORE THAN 30 - 40%. If weather is cold, no more than 10 - 20%.
To get biodiesel WVO needs some chemical proccess (http://www.biodiesel.org/resources/definitions/) , and you can use it 20%, 50% even 100% without modifying your vehicle.