Put a heater in the bucket and crank the heat to at least 86 degrees F, with no fish you can go higher 
Keep it there for at least 2 weeks.
The heat speeds up the life cycle of the parasite so that the tests or cysts or whatever they're called will hatch faster.
With no hosts they won't be able to breed and will die.
2 weeks is the length of the normal life cycle, so by waiting this long you should have caught them all.