DPGerson,
Had the same issue that you are having. Forget the ice, it does very little, you can look that up on the net. Go to Amazon and buy a Valterra A01-0184VP Master Blaster Tank Wand, there cheap.
When you know that your tank is completely empty fill it with hot water and overdose with dawn dish liquid. Let in tank overnight. Drain you black tank, leave valve open. Stick the wand down the toilet with hose on high and keep twisting the wand at different depths. Look at gauge, it should be working. Fill tank again and flush. Problem solved