I pour gasoline on the mound. Kills them instantly. Dissolves their bodies…never to be seen again. You can come back 10 minutes later and dig way down into the mound and find no ants.
I go one step further with the gasoline trick...
Just make sure you have a good supply of water for your garden hose.
That’s the best method we’ve found too. Doesn’t take that much either. I think the fumes exterminate them all the way down into their tunnels.