According to the product claims..... The big clumps of crap are broken down to micrscopic size, passes through the filter and is combusted. If you do a search, one list member took pictures of a primary that had been gunked up (but not clogged). After running the product there were obvious signs of the black stuff gone (partially) from the filter. I too had some specs of black crap in my primary when I first bought my 300D. After running startron Tank Cleaner(64oz) as per directions, the black flecs were gone.
BTW, I'll tell you the same thing I told Hattie. I (personally) don't rely on this product to kill HUMbugs (Hydrocarbon Utilizing Microorganisms). But it seems to work great on asphaltene type stuff.

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04 VW TDI Passat 80,000mi
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