The main ingredient in Drano is Sodium Hydroxide - which is what we use to strip old finishes from decks....so I guess in theory, it might work, however, I wouldn't think that it would be very cost effective. Drano also contains sodium hypochlorite (bleach).
Just in case anyone may be remotely interested in how I know this off the top of my head - we had the drain clog from hell a couple of weeks ago and busted it up with Steve Rowlett's RM2X (sodium hydroxide). I recall a thread somewhere where someone also said that sodium hydroxide was the same as lye - which is in drano
As far as why the guy isn't is business? How would you like to see somebody putting drano on your deck????? LOL Perception matters!
Celeste