When the oil comes out looking good I don't worry about it. It's a 1 micron sock so I would be staggered if anything more than 5 microns made it through. If the oil is ugly I just recycle it. I have too many other projects right now to work on an oil filter system, but it's on the list. Mostly I'm still looking for a good cheap pump, ha ha ha.
Why do you have 8 filters? What are they? Seems excessive. I would not think you would need more than about four, with two of them being cheaper, same-mesh versions of the filters that came after and being there to protect expensive filters from clogging.
My collection/storage tank "this tank only gets known good clean oils" has two cleanable 75/35 micron filters in series, then two 10 micron in series, I do this so it gravity feeds faster.
Then it goes into an upflow setup that I use to clean up any petrol I can find.
This is used to remove sediment, coolant, water, any large particles.
Then that upflows to a 20 micron filter into a mix tank, at the bottom of that tank I run a AMSOIL 2 micron NON BYPASS filter and a AMSOIL full flow filter that is 15 micron absolute, Had these on the shelf, why not use them, they should be able to clean 2500 gallons before changing.
I still also use a 2 micron Racor and circulate the 50 gallon drum 7 times before I put into my tank.
I also use desicant air breathers on my drums and collection tanks so no water or contaminates are sucked in as I pump oil in or out of my tanks.
Sounds like alot but if I get a batch of dirty nasty oil I know it will clean up and run perfect in my truck, so far no issues at all.
Javier