When you need to dispose of a 55 gallon steel drum you can take the 55 gallon steel drum to a scrap yard along with other metal or just by itself.
If you just have 1 55 gallon steel drum that you need to dispose of then the scrap yard may take it for free to allow you to get rid of it.
But if you have more metal to go along with it then you could get paid for the scrap metal and the steel drum.
Or you could post an ad on Craigslist advertising the 55 gallon steel drum for sale or for free and someone will likely want it.
Another option is to turn the 55 gallon steel drum into a burn barrel, wood stove or use the 55 gallon steel drum to put other scrap metal in.
I have a few 55 gallon steel drums that I keep in my garage to put old brake shoes, brake pads, oil filters etc in and then when full I take them to the scrap yard with some other metal and sell the scrap for a little money.
The scrap gets recycled and disposed of properly and I make a little money doing so as well.