I use a thing like the Porkinator, but it was much less money.
Sorry Tony, I could not find the link, but here it is nowhttp://www.porkpuller.com/
I don't do pork butt's often but when I do...Seriously, not a big butt person but when I did 4 for a church meal and was worried about them holding temp for safety I used this.Double wrapped and put inside Cambro and right after service I went out to my truck where I kept them with a clean 5 gallon bucket, and a variable speed drill motor. You can run it full speed for sure but I quickly shredded 4 butts and put in full size pans with lid and served a hot meal. Available at Home Depot for Cheap!