I use an old turkey pot as well. It was scrubbed and soaped up real well. The only problem is since it's aluminum I had to "season" it again by boiling water in it to get the shiny aluminum interior to darken.
It also has a spigot on the bottom of the pot that I can never seem to be able to get clean. My first few beers had an oily film on them. It could have been hop oils or oil from the last turkey that was fried. Not sure, but the beer tasted great anyway!