I have a clear drain tube routed down behind the front bumper just below the airbox capped for periodic draining. This allows me to see how much schtuf is in there. At any given time, I can see a small portion of clear liquid in the stack. I'm keeping a plastic bottle in the garage for all the drainage between a given set of oil changes. It'll be interesting to measure how much is in there when the ticker rolls around again.
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2005 Silver CRD Limited

245/75R16 GoodYear Duratracs
Fumoto drain | ProVent CCV Filter
Stanadyne FM100 filter | Cummins fuel pump
GDE Eco | SEGR | BoulderBars | FrankenLift | Frankenskids