Got a very large decking to clean a week on Monday, its got to be around 20 meters long by around 6 meters wide. 1% hypo? Only have a pump up sprayer so will probably have to do it in sections, been concerned about overlap being cleaner and noticible. Whats the max time I could leave it on? wondering if i could spray the lot fast enough before having to rinse it off, and then obviously would have to rinse in stages? Any advice?