I've used gas in the past but it kills the grass and I ran out of Bifen so that's why tried out the cheap DG dish soap deal, I'm going to keep a sprayer full of water with a good shot of dish soap ready to go from now on, to easy and cheap.
I have used gas, explosives, and anything else you can think of. But recently I just boil a pot of water and pour it down the hole. Done deal. Not even sure where all of the ants that were outside of the hole and didn’t even get burned and flooded go, but they disappear too.
I also tried boiling water and it killed the grass too. I heard or read that if the queen is killed one of the other ants turn into a queen and they just keep on keeping on as there are many ants outside the mound searching for food.
The problem with fire ants is you can 100% kill every mound on your property but they will be be back. On my property it usually takes a few weeks for new colonies to find their way there and it's a never ending battle.