I don't say much this these days, as some of you that are reading this know, but............when it comes to this topic and what people say for what they want I just have to scratch my head.
Time is the best method to filter WMO, or in my case any oil. I don't care if it's gear, ATF, etc.
Here is what I do, and have done for countless years. All the trucks in the quarry, and the haul trucks on the road running between the quarry and the staging yard run 100% "whatever oil" during the warm months. During early spring and going into fall they get thinned to 50/50...."whatever oil"/diesel. This is, of course, the multifuels. The Cummins never get more than 25% regardless of the time of year.
I dump everything into pallet tanks. You guys call them IBCs or totes. You set the tank down so that the drain valve is higher than the opposite side. Say two inches or so. On the opposite side of the valve at the bottom you put some magnets. Doesn't matter if they are from some old speakers or what they are. Just big enough to have some pull. You keep filling that tank until it is full. Then start filling the next one, etc. After that first one has sat with no agitation for a month or two you open the valve so that it slowly drains. I sit mine up on a rack when full and then sit an empty one in front of it when I go to drain. I let it drain for about a day until it's empty, just to give you an idea of the flow rate. When empty you will see a lot of crap sitting in the tank. Flush it out when you are ready to use it again.
I then take the tank I just filled from the first and drain it into one of my steel storage tanks. When I do this it get's filter through three filters in series starting at 50 micron, then 20, finally 10 pushed by a Redline pump. There you have it thousands of gallons of "whatever oil" each year. My actual time is little because I can walk away from it and let it do its thing. Come back to it the next day and move a few things around and leave it again.
I haven't done the books on 2015's production yet. However, for 2014 I went through 3,200 gallons of "oil" with a cost of $82 worth of filters. IMHO that's cheap. And FWIW none of the filters on the trucks were changed anymore than standard servicing dictates.
You guys can do what you want, but I just don't understand why everyone thinks they have to run it through a centrifuge.
Then again, I don't say much these days. Maybe it's better that way. Can I get a men.