Just because you really want this method to be humane, doesn't mean that it is. Sure, it's cheap and easy. Does that make it humane? No.
The only method of home euthanasia that is approved by the American Veterinary Medical Association is C02 gas administered with a regulator. This isn't just everyone's opinion.
C02 does NOT cause suffocation. It's a local anesthetic that acts as a central nervous system depressant. The rat breathes normally, goes unconscious, then dies while unconscious. This is true as long as the C02 is used correctly with a regulator.
Honestly I don't understand why you are fighting everybody on this. Picking up a C02 tank and regulator is affordable and easy.