The Cascade Action Pac is just another packaging variation of a low-sudsing detergent plus a perfume, designed for dishwasher use. When used in a waste tank, no better or no worse than any other low-suds detergent, would be my guess. Any kind of degreaser should help a little, especially in the gray tank where food wastes can build up a greasy residue. You want a low-duds type, so that the tank doesn't froth up when traveling - it can be amazing how much suds you get from even a tint bit of soap in a tank that is sloshed around for 100 miles!
Personally I don't use any of that stuff, but our waste tanks are in constant use, filled and dumped, so they tend to stay "clean". Once a year I may fill the tanks with water and add a healthy dose of a enzyme type septic tank cleaner and let it sit for 3-4 days. That gives the enzymes (yeast bacteria) time to eat their way through any organic accumulations anywhere in the tank.
The old ice cube trick may have some benefit if the tank is filled to about 1/4 with water along with 15-25 lbs of ice. That should let it slosh all around sides and bottom real well. Probably more effective on solids or perhaps strips of poorly-dissolved paper than on greasy sludge, but that's just a guess on my part. The ice trick is one of those mythological campfire remedies that everybody loves but there is only scant anecdotal evidence that it works as a general method for tank maintenance. I don't doubt that it has cured a few and probably can't hurt to try if you have a problem, but it's not something I would recommend as a routine tank cleaning strategy. Just my $0.02!