Board Thread:Questions and Answers/@comment-188.179.113.218-20130520180915/@comment-5627887-20130525233720

I have never seen a randomly spawned pool of Sludge, in my experience it can only be generated as a by-product from MinefactoryReloaded machines like the Harvester etc, however you're right it basically makes the materials for you while you go and do other things. The only time you'd need to get them manually is if you want vast quantities of sand or clay straight away and don't have the patience to put the project on hold and do something else.