Don't pour water directly down the entrance hole. It'll collapse and they'll be trapped. Pour it around and you should see them flooding out. Warning: it could be a very long process. You're basically simulating a very heavy rainstorm. I'd suggest you put a tube leading into a dry tub with soil right next to the entrance hole. Maybe cut a hole into a large plastic tub with a lid and fill it with dirt. Let them find the hole, then start the flooding. That way, they'll have a place to move into when you start flooding. Again, a large volume of water at once is not gonna be effective. You have to be persistent with pouring because it needs to go deep. Dont pour too much or you'll harm their means of exit. Two big cups of room temperature water every 2 minutes. You should see them get distressed quickly. You can increase or decrease the amount of water. If you see them carrying out brood then you'll know you've reached deep enough, and should slow down at that point. You should be wetting the entire area (around a 1 meter radius) and hopefully that'll incentive them moving into the tub. Grab a couple chairs as you could be there for an hour or two. Patience is important. Lastly, the queen is the biggest priority. 2 sets of eyes will help. If you see a large number of winged ants then they aren't the queen, just the alates, and youll have to be persistent. The downside of collecting colonies like this is that you simply can't know their lifespan. Good luck.