Also interested in more data or info regarding not having a clue if the fluid is Synthetic or not as recieved
I have looked into the by products of the pyrolysis of various lubricants, plastics, etc. It appears that Synthetic lubricants are silicon lubricants and their pyrolysis results in similar products as petroleum distillates, so I believe it is a non-issue. You can find my research on that topic at this link.
My premise when making diesel fuel blends out of waste oils is to blend, then settle it for 1-7 days. Anything that does not remain in solution is removed, and the rest goes into the fuel tank after filtration.
In the 6 years that I have been burning waste oils in a diesel engine I have not found an oil that does not burn just fine on my diesel engine as long as it remains in solution through the settling period. The only oil that I have had trouble with is WMO, which tends to coke my injectors. I believe it is because WMO has a lot of ash and soot dissolved into it.
I have also read reports from a large number of people who have been burning WATF in their engines for years without trouble.
The problem that I see with WATF is that it is often contaminated with WMO. So, if you can get the WATF without WMO in it, then you should have no problem burning it on any diesel engine, even un-thinned, but I would add some solvent to it like diesel at 15% or gasoline at 5%, especially in the winter; or run it in a heated 2-tank SVO-like system.
Your original question was how to clean WATF up for fuel consumption. I use a 1-micron bag filter to process all of my waste oil blends, and it has worked great for the 2 years that I have been using it.
I also have a centrifuge, which I am very happy with, but I find most waste oils are not dirty enough to justify buying a centrifuge. I got it for processing WMO, and I find it is very effective for that. Since I now own the centrifuge I then use it as the last stage in my fuel processing, just to make sure all sub-micron particles have been removed from my waste oil blends.