I have been wondering the same thing. Eight years ago I was given a 500 gallon poly tank. I brought it home and use it to store WVO in. My filtering was simple, I used old sweat pant legs as a sock filter. I have been putting oil into the tank all this time and have never pumped off the bottom, always about 12" above. I do a titration every time I brew a batch, it tests between 1.5 and 2.25 over the years. I guess some of the crumbs from 1999 are still at the bottom doing something, but no bad smell has bubbled up yet. I stored WVO in metal drums before the poly tank and I notice a rotten smell and higher titrations over one year in metal drum. I have noticed that biodiesel lasts much longer in poly drums than in metal drums. Get busy and brew your stock and store it as BD. I have noticed that BD seperates after about one year. I just pump it into my reactor and heat it up and give it about an hour of pumping to remix it and then into the tank for use. Reasons to process your oil now and store the BD are cost of chemicals today rather than next year. Another reason is, if you ever need to move and you have 500 gallons of stinky WVO in drums lined up someplace waiting to be processed is harded to make go away than selling the BD for $2.50 and it goes away in a day or two.
