Had trouble finding the recommended product, Liqui-Moly Diesel Purge, so I went with what’s available. A can of Wynn’s Diesel Clean-Up.
Ran the can through the engine and got out some nasty stuff.. Yeow!
Will run some biocide through the engine too, some says the blackness is algae. You now, plants growing in my engine. Won’t allow that, now will we?