I have a 15" Sailfin and a 10" Royal in my 180. The Royal hands down is my favorite fish...and hands down the most "dirty". I can't believe the sawdust everywhere...like a green and black chainsaw! Anyway, still my favorite.
I have found with Plecos in general, they don't make any more mess than any other fish I have had...my Oscar made the most mess by far. The stringy poo is just diet. I feed my Plecos a vary diverse diet, and I have rarely had to clean the stringy poo out. But, when I feed them algae wafers, then its a mess...like they are decorating the place. The key I have found, with all my fish, is moderation. I used to feed twice a day. My fish all got fat. I have reduced their feeding to once every other day, even every third day, and my fish have all gotten much healthier. I have seen normal growth, no disease to speak of and best of all...no messed up tank from poo everywhere.
The Royal is a royal sawdust factory. But I don't mind. I know its just wood and its easy to vac out of the tank. It doesn't affect the bioload as far as I am concerned.