I didnt bother much with the outside of mine, but the insides were terrible. The place I got them pulled the valve out and let the beer remnant dry on the inside for a month in the heat. I scrubbed for 20 minutes and had half of a square foot mostly clean.
Filled it with hot water and some PBW, came back four hours later, everything wiped away to spotless in less than 5 minutes. Perfect.