Hi chap Ive been there and done that in the long run its not worth it. You don't get a good return.
Sorry i couldn't`t help more.
I think the boat has sailed a bit on veg oil too, i used to run my ford ranger on it (25litres oil to 5 litres petrol) i run like that for over 40, 000 miles with no problems but i did full service every 5000 miles. I only used new stuff while it was cheap enough but it's almost as expensive as derv now even from cash and carry etc. I did try filtering old stuff but it is a lot of mess and round here (kent) all the big boys seem to have the waste oil