Why did you think the steel wire handle on a 5 gallon bucket would flush in the first place. It's just a handle man not a flush lever. You will have to empty this "toilet" the old fashioned way.
This hapened to me this weekend, I got some super drano poored the entire bottle in let it sit for 30 min then boiled some water poored the boiling water in as I flushed it and it cleared up