The best results have been to  wash the new cast iron in hot, soapy water twice until you are sure the waxy coating is removed.  Heat the piece for 5 minutes to make sure it is dry of water.  Melt some solid Crisco in a small pan and apply it to the warm iron with a clean, lint free rag, or  good quality paper towel.  Wipe off the excess on the edges.  Excess oil will not carbonize on the surface and will flake off.  Place up-side down in an outdoor grill (if possible, to cut down on smoke in the house) .  Regulate the heat to 425 degrees and leave for 1 ½  hours.  Turn off the heat and allow it to cool.   Apply another coat of Crisco to the iron and repeat the process.  You should have a good hard, black finish at this stage.  A third coat will enhance it to a point that you can cook anything in the DO without concern.  

I have cooked cobblers and several other dishes  without a liner.  Each cleaned easy with hot water and a plastic bristle brush.  I wipe it dry and apply a light coat of Crisco while the iron is warm.  Make sure to clean the ashes off the lid and treat the same way.  You are  ready to cook again.