Why is this important? When you have rats in your attic and put out rat poison, you are more than likely going to end up with dead rats in your attic. And dead rats smell...and attract flies...which lead to maggots.
So your pest control guy insists that it is true that they go outside for water and die? Ask to see the label of the product. If something so genius as this is true, you would think they would advertise it, right? No where can this be documented as true. Stick with rat traps...the simple $3 Victor snap traps...or apply xScentPLUS 🙂