Here are some more images. Having a little trouble finding all the old documentation on this stuff. Some is on paper so if you are really gung ho on doing this PM me and I'll send over some hardcopy of the plumbing diagrams. The looped return on an MB is counter intuitive and I always have to refer back to my notes to see how it works.
Anyhow, here is bad oil. You don't want this. You need to tell your sources you do not want this and you cannot use it. You want the dark black transparent caramel colored oil on top. Not the creamy animal fats that sink to the bottom. If you get an inch of fat on the bottom it's okay. Just decant the good stuff into your filter rig. This photo is extreme. You do not want this disposal problem. I used to compost the white part. It makes rich soil and breeds Argentine ants. Some restaurants fry with solid (at room temp) frying oil. You don't want that. Look at the empty bottles. You want pure soy, pure peanut, pure canola, pure safflower etc.. It'll save you filters and hassle of becoming a waste disposer.
The part line will move with temperature. Some say heat in the sun and clarify the oil before filtering. Others say cool the oil and decant the clear liquid. There are different strategies. I like to decant when cold because the creamy stuff will solidify in the filters and ruin them if they are not heated.
Settle your oil at least two weeks. This makes it easier on your filters. It's amazing how much ash is in the oil. Gravity is free.
Here is my filter system a few years in. Every little drop spilled adds up to a sticky mess. I used cafeteria trays filched from a local college as secondary containment. Lining your floors with cardboard boxes found in the dumpsters helps too. The old oil oxidizes into a sticky resin. I never bothered cleaning up my rig much. The beauty of this rig is that it runs on compressed air. It's silent. You pump up a 5 gallon compressor tank to 100 psi and regulate down to 30 psi and push the air into the BBQ grill tank. It is completely silent once the compressor is off. Run the compressor while you fill oil and set up your collection jugs. Then shut everything down and turn on the air pressure. Go to sleep and in the morning you'll have a full can of clean fuel. This simplicity of fuel prep is going to help you survive the grind of the hobby.
A friend of mine built this interesting recovery/filtration system. She was a starving actress and lived in her Jetta. She could filter a tank of fuel in 30 minutes with this rig. She had very toned arms. The machine is basically two water filters inline with a barrel pump from Harbor Freight. It worked well for a person without a home. She was (and still is) attractive and found it really easy to set up connections with restaurant owners to pick up oil. I couldn't find the photos but I have one of her in coveralls hunched over this contraption in an alley pumping oil. It was quite a sight. The hobby got me some very interesting connections over the years.
I got this air tank on Craigslist free and made a vacuum recovery kit from it. You basically seal up the tank and put a hose with a ball valve on it. You pump down the tank to 28mm Hg with a cheap vacuum pump. Some people use an old fridge compressor. I had a real vacuum pump lifted from my work. Dip the hose in the dumpster and open the valve. The oil goes right into the tank. Fast. I could drain 20 gallons of top oil in thirty seconds. Silently. Try that with an electric transfer pump. This was important because dumpster diving can get you in trouble with cops, renderers and restaurant owners. Again another system where you store energy up using pneumatic power.
In the car with an integrated filter. I got tired of lifting the tank in and out of the car because it was heavy. So I just hooked up the compressed air and filtered it in place. Note the little drip tube going into the fuel cap. Now you don't have to lift jugs/tanks in and out of the car. Less work. Remember, getting smart about it? All I had to do was remove the empty tank from the car the next day. Or, leave it in place for next week's dumpster dive.
Typical plumbing to build this kind of gear. Luckily I worked in a science think tank so this stuff was everywhere for the taking. Basically you need tubes, fittings, valves and hose clamps. The only tricky valve is the Pollak three way but you can get this online or in a junkyard off an old two tank truck. Using an outboard motor boat tank from Walmart I think everything you need to convert will cost less than $60.
Here's a pro tip. You will go through several fuel filters on your car a year. They will gradually clog enough so the fuel pump cannot keep up with the restricted flow rate. So when you replace the filter, just put it inline with your filter rig in your garage. Now you have a sub 3 micron filter. Your garage rig can generate more pressure than the car's fuel pump so you will get many more weeks of use out of the "clogged" filter. The more it clogs the better it cleans too. So the expensive car filters (I used VW Rabbit Diesel filters because they were cheapest) are used twice.
My advice to anyone just starting out is just buy the cheapest running MB diesel you can find. Try under $2000. Don't convert it. Mix in 20% new soy oil from Costco into the fuel and drive the car. See if you like it. Then build my filter system and start collecting oil. The cheapest collection pump turned out to be a one gallon milk jug with the top cut off. You can dip ten gallons off the top of a dumpster in less than twenty seconds in pure silence. Just cut the neck off the jug and use it like a ladle.
Filter this oil. It should be easy if you dipped off the top of the barrel. Dilute your fuel and drive. Unlike new oil this will clog your filter sooner or later. It depends on how good you are at filtering. When you start out it will be sooner. Make sure you have a clean filter and tools in the trunk. Make sure your priming pump on the car works so you can purge the air while you're on the side of the road. And don't drive it bad neighborhoods where you won't want to pull over and change a filter in the street.
This is why the two tank system is so good. When you clog your oil circuit you just hit the diesel switch and go back to diesel when the car starts stammering. There isn't always a lot of warning when the car starts to stall especially if you're moving quickly down the highway. My poor wife got really accustomed to the stammer and my hand darting out to hit the diesel switch during our years of road tripping in my bio Benz. This is just part of the game. An alternative trick is putting a one gallon tank upstream of your filter that you switch over to when you get in trouble. I figured if I did all the plumbing why not have a whole tank.
Ok, hope that helps. So bottom line I suggest beginners one tank with mixed fuel in a warm climate. If you like it then you can delve further in. I pissed away over a decade doing this. Not terribly interested in starting up again.
One cool thing is you get good at chatting up cooks and cutting deals. I also met some really colorful people in the biodiesel movement back in the Bay Area. Once you learn how to convert a car you get a lot of bartering opportunities with people wanting cheap conversions.
And no this isn't technically hard. It's actually really simple. The hard part is maintaining the car, maintaining restaurant connections after management changes and moves, and keeping your oil clean.