Diamond Rat Killer is grains coated with 2% Zinc Phosphide. Both rats in my house died almost immediately after consumption. It is useful to notice the habits of the rats and ensure no food or water available for them in the house for days at a stretch before using the bait. Then they're sure to go for it.
It is useful to place the bait along their usual route in and out for the house. I placed it a coupla feet from their hole in the house. Be sure not to handle it with bare hands and dispose of the bait where animals cannot eat it. Less than 10g took out an adult rat and its offspring.