I, like pigpen60, thought filtering any waste oil down to 1-micron was overkill, but then I had chronic coked injectors after only 3 days filtering my WMO blends down to only 5 microns. So, I added the 1-micron bag filter. It helped, I got 1-4 weeks on those blends before my injectors coked solid.
But, 1-4 weeks on WMO blends before my injectors coked solid, was not good enough, so last year about this time I bought a centrifuge, it helped a lot. I got 1-2 months of running on 80-20 WMO blends before my injectors coked shut.
I was amazed at how much crud came out of my centrifuge bowl after blending, settle WMO-gasoline blends for weeks, then filter through a 1-micron bag filter. So, I was happy to add the centrifuge into my fuel making operation.
Since then, I have stopped burning WMO, because my engine would still coke its injectors on only 20% WMO-blend in my fuel blend, but I keep using the centrifuge in making my WVO blends, because it is now part of my waste-oil fuel making operation, and it removes enough particulate from my WVO blends to justify keeping it in the loop.
I figure waste oil fuel blends can never be too clean. So, I am now working on a WMO distillation system, and what little distilled WMO I have run through my engine has not posed any problem at all so far. However, I am still developing and testing.