You don't need chemicals. You don't need Calgon. You don't need ice. You don't need anything but water. Seriously folks, ice cubes in your tanks? How long do you think these will last before they return to their original state of water? Dump those bags in there and very, very quickly start driving with lots of lefts and rights and stops and starts to get these cubes to scrape your tank clean.
You likely have the same odds of hitting the lottery with this scenario as you do with this method cleaning ANYTHING current stuck to the walls of your holding tank.
Fill your tank, drain your tank. The rest takes care of itself.