Over at
Infopop where much BioD discussion goes on the most common route seems to be filter bags. I know Greasel.com sells them and they are also available through various industrial supply houses.
I am running veggie/gasoline/cetane boost blend right now that I filtered through a five micron undersink water filter. I get my oil in cubees so I rigged up a cubee lid hose adapter that allows me to connect a full jug of oil and plunk it on a shelf above the filter. Pace is slow, maybe 2 gallons per hour but I'm involved for only a few minutes per jug so no big deal.
I just got my mail order bags and have yet to rig them into a gravity driven filter. I attempted to build a sand filter at first, dear lord what a mess. My (limited) understanding of the WVO thing is that you should filter it to 5 microns or better before you put it in your wheels. You should also blend it before you put in your tank. I am using a hand pump to mix mine in a 45 gallon drum.
If you have solid grease I have no idea how you process it, mine is liquid. I am carrying a spare fuel filter with me now "just in case".
Glenn
86 F250 with an astounding 160 kms on veg (that's 100 miles :-) )