No hole in the bucket. Just a submersible pump which I got at a hydroponics store.
Like this 
https://www.amazon.com/EcoPlus-728310-Submersible-Pump-396GPH/dp/B0018X2XT4/ref=sr_1_1?ie=UTF8&qid=1470237372&sr=8-1&keywords=hydroponics+pump
Pipe or tubing goes on the pump and out the top of the bucket. Just need to loop the other end back to the bucket to be reheated. Pick a pump based on the height difference of your bucket vs your nipples to make sure you'll get some flow. I used flexible tubing and just zip tied the open end of the loop to the tube coming off the pump to aim it back into the bucket.
I tried an aquarium heater in a regular 5 gallon bucket before the heated bucket and it did not heat the water enough. Froze in the lines. So I found the heated bucket and moved my setup which just involved replacing the bucket.