I also make bio when it's hot outside. Like Diesel Power I have "found" most of my materials for processing. I use a 40 gallon heavy plastic mixing tank I found at a used restaraunt supply house. I use an old 1/2 inch variable speed drill with a home made mixing shaft, and use an electric charcoal lighter to heat the stuff while mixing. I also use the 20% methanol mix but have found that 15% works just as well MOST of the time. From experience I can tell if I need to add the other 5% as soon as I start the mix. Yield will be almost exactly what you start with minus the amount of methanol. IE, start with 30 gallons of used oil and add 10 gallons of meth you get back 30 gallons of good fuel, 10 gallons of soap. The soap I give to people who make it into bar soap, use it as is to degrease stuff, use some to clean my tank after making a batch, and flush the rest if need be. It is just soap so no big deal. I get my oil from a local Checkers and from a local small seafood place. Both are happy to give it to me, but you have to ask first. It used to be that the waste haulers paid for this stuff but now they charge to haul it away. Oil from Checkers is not heated as much as the stuff from the seafood place and as a result I get a nice golden colored fuel that smells like frech frys when I run it. The seafood oil is dark in color but smells the same when burned. When running bio the car does not have as much diesel clatter, starts faster, but gets a little less mpg. I filter the fuel through a 20 micron filter first, then a 5 micron to the tank. Fuel filters on the car are OEM and last just as long as with dino fuel. You need to replace all rubber fuel lines with OEM rubber as the meth will eat normal rubber. Bio has been used in Germany for 20 years so these cars are made to burn it. Mercedes fuel line will not get soft on you. Cost besides my time is about .65 per gallon. Biggest cost is the methanol at 2.50 a gallon. Usual mix is as follows...

30 gallons waste oil
10 gallons methanol mixed with 30 grams of lye
start mixer, dump in lye/meth mixture
start heater
mix for 1 hour
stop mix and heat
let sit for 8 hours to settle
drain soap from bottom
let sit 24 hours
drain about 2 more ounces of soap
filter to 20 microns
pump from holding tank to car through 5 micron filter

I started with this website

http://www.dancingrabbit.org/biodiesel/flrecipe.html